Being slim isn’t a bad thing. Wilder’s problem is partly that he’s been protected and he also just can’t box. Fury has never loaded up on power like he did last night and Wilder wasn’t expecting it at all.
He was done as soon as he landed his right and Fury just shook it off. Honestly I think he was done as far back as the last fight when Fury got up. Had to be in the back of his mind that he just can’t keep Fury down