Aside from Chisora, who is the best/most durable opponent that former kickboxer and MMA fighter Whyte has KO'd with his left hook? I think the answer is former kickboxer and MMA fighter Lucas Browne, who started boxing at 29 or so. Needless to say that Ngannou was a far better MMA fighter and striker than Browne.
I would back the top 50 heavyweights (maybe even the top 75) to beat Ngannou. The guy is a great MMA fighter but he's not a boxer. There's a reason Fury cherrypicked him besides the money.