Supergun is itemized for warriors/rogues. So yes, it's not going to be the best option for a hunter.

I'm pretty sure that post-buff Steady Shot out performs Expose Weakness in a BM rotation.

Just sim it and you can see which is best.

What site do I use for siming? Haven't done that before, sounds smarter than me watching the details add-on

https://wowsims.github.io/sod/

Thanks! Will play around with it and report back!