Its his height that will probably really affect him at HW. Hes 6'3". Add another 3 inches and 15 pounds and he would fill out the HW division better. I dont think his frame is too thin for HW. Actually Gassiev looked too thin for HW. Usyk has got big shoulders and a powerful midsection.
At first they seemed similar, but if you really focus on comparing the chest and shoulders, Wladdy makes Usyk look like a little, undeveloped teenager... Although Wlad is a big, well-muscled guy, even by HW standards.
Povetkin is more sturdily built. 225-230. If Usyk fills out and puts on 25 to 30 lbs. he may do fine.
It is hard for most of us to comprehend just how big these guys are. I remember in high school when I attended a sports camp in LA and Paul Westphal was dunking the ball with one in each hand, at the same time. Merlin Olson's brother was also there. His calves were as big as my thighs. I have seen Johnny Bench around town. Freakishly big, even though he is not that tall. Bill Walton had calves the size of grapefruits. These elite athletes are elite for a reason. They are freaks of nature.
guys like wlad are rare. he is 6 1/2 feet of functional muscle, nervous system and coordination. he would of made an all pro tight end in football.