This is actually super interesting. Big Bang isn't fast, but what he lacks in speed he makes up for with above average boxing skills and exceptional timing and countering ability. And that power is huge. Usyk decision is the logical pick, but Big Bang can take him out.
Prime Zhang lost (via KD) to a green Joshua. Usyk would run rings round him, the way he did all the other big lugs he fought in the WSB.
Usyk wins by a wide UD. Wouldn’t be surprised if there were a couple of scary moments though with Zhang’s sharp power.. But Usyk has a chin.
This version of Zhang would knock out this version of Usyk, Zhang is a fast and tricky lefty and is too big for Usyk who wouldn't handle a fighter who doesn't hesitate to punch...
Zhang did well vs Joyce and Hrgovic but Usyk presents a very different challenge. Usyk is far more agile, faster and harder to hit that either of them. Zhang's movement isn't great and he isn't quick, Usyk would run rings around him and win a clear decision.
It's hard to see a path to beat Usyk without a very good 12 round engine and Zhang was fighting in spurts after 6 against Hrgovic. Zhang isn't a prolific body puncher either and he's pretty lumbering.
Prime Usyk was at cruiserweight and, to be honest, I have no idea if prime Zhang is right now or sometime in his past which I know nothing about. Based on skill levels I'm going with 199 pound Usyk by decision.