I thought he looked very vurnerable in the Wilder rematch, especially when his stamina deteriorated in the second half of the fight... Wilder just didn't have the skills to do anything.
Taking angles on his back foot and looking a bit slick like Floyd Mayweather or James Toney worked well against the shorter, slow-footed, one-dimensional, plodding, brawlish Dereck Chisora. He wouldn't be able to do that against Anthony Joshua, let alone Lennox Lewis.
He was letting his lead hanging against Chisora, that's how much he felt threatened... He wouldn't do that at any point against Lennox, whose right hand was just as devastating as Wilders, plus much better boxing skills.
Fury's a little taller, you're right. But I think I know what Lennox response would if he was confronted with that fact in an interview: "He'll realize how tall I am when he looks at me from the ground".