On one hand I agree with you gnash. On the other hand, when hoyfield etc moved up, they were fighting really good heavyweights. I can quite easily see usyk being heavyweight world champion.
I don't think it's just the size difference. Take tyson, 5'10", hammered a few fighters that were 5, 6, or 7 inches taller than himself, and was outweighed in almost all his fights. Can't see usyk having too many problems beating todays heavyweights