Remember this guy:
Zhang is too much risk for little reward and is a dangerous opponent. I don't know if AJ gets smoked by Zhang, but there are many constants in Joshua's career and fighting style that make that a fight to avoid unless necessary than there are that say he could take the guy to the cleaners and continue along whatever path he's establishing for himself.
Your points one by one:
- Joshua does not move his head well. He might not be Joyce levels of stiff and stupid (to block punches with his face), but he struggles a lot with getting his head off centre line, which is really bad against fighters who are game and throw good hooks in particular, especially with how Zhang mixes in his left straight either in combinations to initialise or to finish - Joshua is primed to get hit by something in those barrages with his lack of natural movement.
- Zhang has more stamina than Joshua. I think you're suggesting Joshua would wear him down with shots and tire him out that way as opposed to Joshua simply having the bigger tank? Zhang is no slouch in exchanges; Joshua does not do well with getting hit - exchanges are much worse for Joshua than Zhang.
- You've mentioned Joshua's power, but not Zhang's. Zhang hits hard, he hits in bunches and he is more than game to stay in the pocket and bang. In an all out war of that kind, I'd back Zhang because Joshua's punch resistance isn't good (to say the least) and nor is his movement. Pot shotting heavy, cautiously and long is an obvious route to victory for Joshua, not trying to mix it up with a better brawler with a superior tank and punch resistance.
- Zhang is extremely game, so much so, he's exactly the kind of fighter all of those at the top of the division should actively avoid if they are being risk averse. He would go to war with anyone in the division and I don't think he comes up short in a fire fight against anyone - the avenue to beating him is staying safe and outboxing him, which is what would be expected of Fury and Usyk. Joshua? Not so much, as he has much worse head movement, concentration and manoeuvrability than those two.
I'm not saying Zhang beats Joshua, but I would say it's a fight Joshua should avoid because it is wrought with danger for him and he gives Zhang more opportunities to capitalise than Usyk or Fury would. Joshua has nothing to prove vs the likes of Zhang and is well beyond the stage of having to show what he's about. His redemption arc is about looking like his old self before the fella at the top of this post destroyed his confidence, and then pursuing a few mega fights to maximise his earnings and legacy before calling it a day. Zhang can't really do anything to interfere with that path or to interject as there's so few at the top of food chain to chase, and between those top 3, there's tie ups throughout the next 18 months with rematch clauses and whatnot. Joshua probably needs another statement victory like tonight's before he can really start to call out Fury (assuming he wins vs Usyk), which most likely does not involve a risky entanglement with a fighter like Zhang. I'd bet the Saudi's would pay for N'Gannou vs Joshua well before they'd entertain Zhang, too.