He's a nightmare matchup for Usman, even if Kamaru could take him down it wouldn't be easy atall and Colby exposed you can gas Kamaru if you make him work like that.Chimaev would have the best shot at Usman but his takedown defense hasn't really been tested yet
He compensates for it well but Usmans knees are gone, he cannot do road work and if you watch majority of his training footage he's always wearing knee pads because he has almost no cartilage in his knees.
I can see retirement in the next year or two