He's an ATG at CW don't know if he's a top 100 ATG though. If he beats AJ he will be a top 100 ATG or better no doubt about it.
I don't think Holyfield ever legitimately beat Bowe or drew with Lewis, these fights were also on neutral ground and at home respectively so he didn't have to deal with the "B-side" disadvantages that Usyk does. Moorer was a blown-up light heavyweight who lacked power and had serious chin problems at heavyweight, especially by the time of the Holyfield rematch. Holyfield is still the gold standard for cruiser-heavyweights because he gave the best account of himself against elite super-heavyweights (better than Haye) and had a number of decent/good wins at heavyweight. But If Usyk was to school or stop a prime AJ while several years past his prime and up against British Matchroom corruption, that would be the best ever cruiser-heavy win and by some distance.