I think Zhu had plenty of help from her team-mates in Rio. Sure, she was the star player and deservedly MVP, but her team contributed a lot. If Kim was Chinese and Zhu was Korean, I think we would be talking about how Kim led her team to Olympic Gold.
That said, I'm not saying Kim is better than Zhu or Zhu is better than Kim. They are both great. Zhu is a better blocker and maybe better spiker, but I think Kim has the advantage in passing, defence and serve.