Fury would have a lot more success than Joshua, he's just more savvy and experienced in a boxing ring. Uses his weight, leans on people, roughs them up.
Usyk is top class, but likes of Chisora made it a tougher night for him. I do feel sorry for him though, he was built up by Matchroom as some unbeatable, all time great and the reality is he's a fantastic athlete learning on the job, which was evident throughout to people who really follow boxing. It's like even he doesn't really know what kind of fighter he is.
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.