AJ has become a meme recently but despite not being a top fighter he is very talented. He lacks the flair and variety that all top fighters have and is too robotic, which is what holds him back, along with his chin/tank, but he is no walkover.
His hands are deceptively fast for a big man, he has a lot of power, great fundamentals and of course great size. Usyk beating him twice in a pretty convincing manner both times is nothing to scoff at and at the least says he would be competitive with Fury.
Fury can use his weight and try and be rough but these are not tactics that really work with fighters like Usyk with excellent positioning and ring IQ. Indeed Joshua tried many times to grab him into a clinch and rough him up but Usyk was wise to his attempts and pushed him off or slipped.
Additionally we have previous history suggesting Fury struggles with smaller guys who can throw good combinations. Cunningham/Wallin/McDermott all gave him big trouble and Wallin (who is a no name with pillows for hands) nearly took him out. Fury's best performances have come against bigger guys evenly matched in size (Klitschko/Wilder).
I would also say, Usyk is not as small as is made out at all. He may not be as shredded as AJ or as tall as Fury but he is rock solid at 6'3, big wide frame that can take a good few punches as he's shown vs Joshua, Chisora and Gassiev.
Fury to me now is better than ever, used to hate his style when his uncle trained him. Way too negative and defensive, did not utilise his size at all and was quite easy to hurt. That Canadian guy dropped him as well, who's name escapes me now. That Usyk I would favour to beat him without doubt.
Under the Kronk style he is a different animal. The Wallin fight was ugly under Ben Davidson but he did have to navigate that horrible cut too.
Usyk is obviously not small by your normal standards but the guy was fighting Shawn Porter and Korobov at middleweight in the amateurs back in his early 20's so it's more by development than design. Korobov actually stopped him once and he's been hurt a few times too.
Beterbiev has dropped him on more than one occasion (although he's a beast so no shame there).
It was on a knife edge vs Marius Bredis, he got dropped by Medgidov too and Glowacki put him down also.
I think Usyk is class but he's just slightly too small for me and lacks the proper concussive power for that to be mitigated.