Probably more to do with the end of Fury's own prime and a lack of motivation imho. Wilder was one month removed from 36 years old in the Fury 3 fight.
you're actually mirroring my thoughts, I thought about putting Breazeale but with it being only a 2 minute fight, we never really got to gauge what he looked like, he just swung and connected. Pretty much like how people thought he may still be serviceable after Helenius, we never really...................saw............him.
What makes me laugh though is that after Wilder KO'ed Helenius most him had as a favourite over Joshua there was no talk of him being a shot fighter then. I agree inactivity and the beating vs Fury would've took something out him. But you can also say the 3rd Fury fight flattered Wilder as Fury was in terrible shape he weighed the same as he did vs Ngannou for reference. And you can also say that no version of Wilder would necessarily be a favourite over the fighters he lost to either like Parker, Zhang.
Fury beat whatever was left of Wilder's prime out of him in the second fight. Wilder had one more world class performance, Fury 3, but he has been severely declined/shot ever since.
Fury took his soul, completely brutalized him, took his masculinity, spirit, invincibility and confidence.
Hard to say considering he spent so much time fighting non-elite opposition before he finally stepped up, and every time he DID step up he either struggled or lost.