Size matters. Much of what LWs say about Khabib is how strong his grip strength is and just him being stronger than they anticipated or using his weight well. He's not the strongest dude, but uses it well. Now, you have to deal with usman where you won't have that strength advantage or it being a neutral attribute. Usman will be the bigger man. You'd be dealing with more resistance. I think khabib could get it done possibly man, I really don't know. Grappling a dude that outweighs you by 20lbs for 25mins is something I'd like to see. I would have liked him to face usman and potentially beat him. I never cared about this gsp stuff. But usman and him are friends and khabib had no interest in moving up, so there's that.
I think skill for skill, khabib is better in all facets of the game. Better striker, better wrestler, better grappler. Better at controlling pace. Better footwork. You name it all. But size is a big issue.