yes, for a guy who started boxing far too late, joshua acomplished some truly amazing things. wilder also won a medal in the olympics and the world HW title despite having started boxing years AFTER joshua. Neither of those guys had any business being anywhere near as successful as they were considering what they had to overcome.
but that's not my point, and you know it. they were still very incomplete fighters BECAUSE of their late start and lacked the foundation to sustain championship level performances because of it.
and as for usyk and his 350 amateur fights, since when does fighting 3 rounds with headgear protection and all kinds of safety precautions cause wear and tear on fighters? in fact what it did was it gave him a safe way to accumlate hundreds and hundreds of rounds of technical skills and experience, while, at the same time, being largerly protected from physical damage. that was a huge advantage he enjoyed over guys, especially older guys, who turned pro after much shorter amateur careers.