Because of the attack types.
BB wasnt screaming against Ace for nothing, why are you down playing Ace now huh? All to make Law look much better than what he is?
Again why is it a mid diff?
The fight literally just started, Teach hasnt used a single Yami technique on Law yet and you expect him to beat him already? He just used two quake moves, one mid air and the other to block a KROOM.
Just look at Rooftop fight with Dragon Kaido getting battered by Supernovas... I doubt you'd say any of it is mid diff bcs "Kaido didnt beat them already".