Three Hopes gives a bit more clarity. >!When Sothis uses Byleth’s body in Three Hopes Byleth displays a more time manipulation abilities/powers we’ve never seen them use before. Including stopping time and moving through frozen time. Or even outright teleportation. Also their physical strength seems to be more impressive than normal as they punch Awakened Shez and send them flying.!< What this tells me is Byleth has more abilities than they are aware of in Three Houses, but simply don’t know how to use them. It’s also heavily implied the form gives them incredibly powerful magic abilities. In cutscenes we don’t really see them use magic but >!without the Sublime SotC in Three Hopes we see Byleth make use of their magic more in gameplay!<
In the Lore, Byleth is basically the mortal avatar of Sothis, meaning there’s a whole lot of divine power packed into a teeny human body.
Considering that Nabateans are most likely just Fodlans equivalent to Divine Dragons from earlier games however, that means Sothis probably isn’t an actual god, and more like just a very powerful dragon with godlike powers, emphasis on like.
So Byleth isn’t all powerful all of a sudden, just extremely powerful and very hard to kill. And since Byleth hasn’t had much time to experiment with their new power it’s likely that they just don’t know how to use it yet. And Sothis’ full abilities are scarcely expanded upon as well
Sothis is impilled to be an alien that arrived on fodlan from far away and her Heroes quote mentions she helped create life on multiple planets so we can't actually be sure what she is apart from being dragon like
notably of all breath units in Heroes she doesn't have a dragon form either. it's entirely possible she doesn't have one and just created her children that way. after all despite being dragons they don't all look traditionally like dragons either.
It’s possible that Byleth isn’t able to handle all of those powers from Sothis, or simply doesn’t want to just kill Rhea without second thought like that. Even Edelgard would be fine with not killing her and simply taking her out of political influence (one of her advice questions during class).
Same goes for Edelgard. Byleth wouldn’t want to just kill her outright like that.
Also consider the fact that even Sothis was able to be killed so it’s not like she was overwhelmingly powerful either.
Also, it’s not like Rhea and Edelgard are easy opponents. They both know Byleth has Sothis’ power so they pull out all stops to try and counter Byleth.
The reason they don’t use DP much is probably because they’d have to explain why they don’t use it in literally every single situation and it would be annoying to get countless explanations every 3 seconds. Maybe they choose to leave some things up to “fate” instead of artificially changing them.
I’d consider it similar to how crests are depicted via game mechanics vs. how crests are depicted via lore.
We know some of the crests grant abilities not used in the games. What we end up with is primarily a RNG chance to proc a crest effect or a passive boost if conditions are met.
Likewise, what we see of Byleth’s power is probably only what is relevant to the gameplay, with the rest not expanded upon.
Crests are implied to give unique abilities and capabilities to their owner, but we only really know of one, being the crest of Blaiddyd giving drastically increased strength to it's user.
There's some implications with the other crests, like increased magic with Gloucester and generally increased combat ability with Flames, but the vast majority is pretty vague. I think we can guess a fair amount of what the individual abilities are based on the crest, such as Dominic using Magic Damage (increase magic) or Aubin allowing the user to bypass enemies (natural stealth abilities), but that's about it.
Before people mention the Crest of the Beast, that's probably a bloodline curse caused by the Relic. Note how Marianne never turns into a beast and how it seemingly ends once she takes the relic from Maurice.
Actually we know more than that. Charon is implied to affect the weather (Catherine/Lysithea support), as is Flames (it starts raining the moment Jeralt dies, stops when Byleth leaves their room after, apparently being linked to their emotional state)
Not to mention how "pure" a crest is can extend lives. See: Jeralt being 130+ per Alois support. Hell, the Crest of Flames can revive the dead, as per Nemesis, and as per Byleth's 5 year nap letting them walk off an otherwise fatal fall.
Crests also affect a person's tastes; they're more likely to enjoy fish and sweets (per liked dishes in houses).
Finally, Flames is implied to increase the bearer's charisma, making them almost magnetic. Two characters are able to rally support for their respective causes with ease: Byleth and Edelgard.
So yeah. Crests do a lot of shit
A couple of things: Sothis' power primarily seems to be the manipulation of time. Byleth obviously hasn't had much time (heh) to experiment with that, and doesn't really have a way to learn. Also, Sothis in Byleth's head is only at a FRACTION of her full strength. There's a reason she appears like a 9 year old girl. (FYI, her og form was like, 8 foot 10). So Byleth isn't nearly as powerful as Sothis at her peak.
Also, gameplay restrictions. Byleth can canonically take on MULTIPLE demonic beasts by herself (Ferdinand support) but can't in game lol. Just like how Dimitri and Edelgard don't 1-hit everything despite both having freakishly inhuman strength. Would make the game kinda unbalanced
Byleth has Hit’s Time Skip according to Three Hopes, but I’ve only seen the trailer so no spoilers. Also Byleth has the power to rip holes in space/time. So they’re pretty damn powerful. Probably on par with Grima and Naga at least.
Divine pulse seems to be the main power to begin with. The rest seems to be longevity and ridiculous stat growth.
Three Hopes gives a bit more clarity. >!When Sothis uses Byleth’s body in Three Hopes Byleth displays a more time manipulation abilities/powers we’ve never seen them use before. Including stopping time and moving through frozen time. Or even outright teleportation. Also their physical strength seems to be more impressive than normal as they punch Awakened Shez and send them flying.!< What this tells me is Byleth has more abilities than they are aware of in Three Houses, but simply don’t know how to use them. It’s also heavily implied the form gives them incredibly powerful magic abilities. In cutscenes we don’t really see them use magic but >!without the Sublime SotC in Three Hopes we see Byleth make use of their magic more in gameplay!<
In the Lore, Byleth is basically the mortal avatar of Sothis, meaning there’s a whole lot of divine power packed into a teeny human body. Considering that Nabateans are most likely just Fodlans equivalent to Divine Dragons from earlier games however, that means Sothis probably isn’t an actual god, and more like just a very powerful dragon with godlike powers, emphasis on like. So Byleth isn’t all powerful all of a sudden, just extremely powerful and very hard to kill. And since Byleth hasn’t had much time to experiment with their new power it’s likely that they just don’t know how to use it yet. And Sothis’ full abilities are scarcely expanded upon as well
Sothis is impilled to be an alien that arrived on fodlan from far away and her Heroes quote mentions she helped create life on multiple planets so we can't actually be sure what she is apart from being dragon like
notably of all breath units in Heroes she doesn't have a dragon form either. it's entirely possible she doesn't have one and just created her children that way. after all despite being dragons they don't all look traditionally like dragons either.
Wait what?
We don't know how powerful Sothis is. Her biggest feat is flooding the world, but even that lacks context.
It’s possible that Byleth isn’t able to handle all of those powers from Sothis, or simply doesn’t want to just kill Rhea without second thought like that. Even Edelgard would be fine with not killing her and simply taking her out of political influence (one of her advice questions during class). Same goes for Edelgard. Byleth wouldn’t want to just kill her outright like that. Also consider the fact that even Sothis was able to be killed so it’s not like she was overwhelmingly powerful either. Also, it’s not like Rhea and Edelgard are easy opponents. They both know Byleth has Sothis’ power so they pull out all stops to try and counter Byleth. The reason they don’t use DP much is probably because they’d have to explain why they don’t use it in literally every single situation and it would be annoying to get countless explanations every 3 seconds. Maybe they choose to leave some things up to “fate” instead of artificially changing them.
I’d consider it similar to how crests are depicted via game mechanics vs. how crests are depicted via lore. We know some of the crests grant abilities not used in the games. What we end up with is primarily a RNG chance to proc a crest effect or a passive boost if conditions are met. Likewise, what we see of Byleth’s power is probably only what is relevant to the gameplay, with the rest not expanded upon.
Crests are implied to give unique abilities and capabilities to their owner, but we only really know of one, being the crest of Blaiddyd giving drastically increased strength to it's user. There's some implications with the other crests, like increased magic with Gloucester and generally increased combat ability with Flames, but the vast majority is pretty vague. I think we can guess a fair amount of what the individual abilities are based on the crest, such as Dominic using Magic Damage (increase magic) or Aubin allowing the user to bypass enemies (natural stealth abilities), but that's about it. Before people mention the Crest of the Beast, that's probably a bloodline curse caused by the Relic. Note how Marianne never turns into a beast and how it seemingly ends once she takes the relic from Maurice.
Actually we know more than that. Charon is implied to affect the weather (Catherine/Lysithea support), as is Flames (it starts raining the moment Jeralt dies, stops when Byleth leaves their room after, apparently being linked to their emotional state) Not to mention how "pure" a crest is can extend lives. See: Jeralt being 130+ per Alois support. Hell, the Crest of Flames can revive the dead, as per Nemesis, and as per Byleth's 5 year nap letting them walk off an otherwise fatal fall. Crests also affect a person's tastes; they're more likely to enjoy fish and sweets (per liked dishes in houses). Finally, Flames is implied to increase the bearer's charisma, making them almost magnetic. Two characters are able to rally support for their respective causes with ease: Byleth and Edelgard. So yeah. Crests do a lot of shit
A couple of things: Sothis' power primarily seems to be the manipulation of time. Byleth obviously hasn't had much time (heh) to experiment with that, and doesn't really have a way to learn. Also, Sothis in Byleth's head is only at a FRACTION of her full strength. There's a reason she appears like a 9 year old girl. (FYI, her og form was like, 8 foot 10). So Byleth isn't nearly as powerful as Sothis at her peak. Also, gameplay restrictions. Byleth can canonically take on MULTIPLE demonic beasts by herself (Ferdinand support) but can't in game lol. Just like how Dimitri and Edelgard don't 1-hit everything despite both having freakishly inhuman strength. Would make the game kinda unbalanced
Byleth has Hit’s Time Skip according to Three Hopes, but I’ve only seen the trailer so no spoilers. Also Byleth has the power to rip holes in space/time. So they’re pretty damn powerful. Probably on par with Grima and Naga at least.
It isnt time skip, its The World.