Say Buuhan trains for a few hours...

What's the strongest opponent he'd be able to beat under DBS logic?

I don't know. Does the fact that he'd absorbed Gohan mean he already inherited his physique and fighting skill? He did get Piccolo's intelligence, after all...

Yeah, he would inherit the Mystic Gohan way of getting stronger as Super showed with having him absorbed, which was why I made this. Thought it might make an interesting discussion. Good point on having Piccolo's intelligence too, despite that he lost his cool against Vegito which Piccolo wouldn't do against an opponent...

SSJ Blue Vegetto.

I'd say he'd be able to handle Base Hit (no timeskip). Train a few days and he'd be able to handle SSJ Rose Goku. Train for a couple of months and he'd be able to handle Beerus.

Quickly on a level of SSB Goku.