Wlad Zhang has serious power but the issue that people have with him is that he is a southpaw and hence they can't anticipate his punches. The punches you don't see coming are the ones which will hurt you more because you can't mentally and physically brace yourself for the impact. Wlad was a freak. People could see his punches and still get ko'd. I dislike Wlad immensely but he was a freakish puncher. Zhang, in terms of power is 9 or 9.5 out of 10 which is excellent. Wlad is a 10/10. Zhang is trickier to defend against because he is a rare southpaw who also throws a right hook - something that very few HW southpaws do.
Let me put it this way: If Ingrid Pitt said she'd let me touch one if I just said Zhang, when real world consequences and the meaning of life is at stake, I'd do it, because there's just not that much in it.
Wlad and also, two-fisted power. He could take you with a hook or a right hand, whereas Zhang is simply a straight left guy.
I don't normally disagree with you often but I have to disagree with you here. Zhang can take you out with both hands aswell he took Joyce with a counter right hook.