His problem seems mental more than anything, as he himself said in the post fight interview. He has been at it for a while and his knees are shot but when he really commits, he does look like the Usman of old. You could see it in the third Leon fight as well, when he wanted to press the action, he was able to but most of the time, the dude looked wary. In the Khamzat fight, he looked hesitant in the first but you could see him build confidence as the fight went on.
That said, mental block aside, dude is still legit. His last two losses were razor close and even at 36, idk, I think he's a top 5 MW.