"Position of power" is a bit of a stretch when we're talking about two high-ranking execs who presumably make tens of millions of dollars. I doubt there's any problem related to consent / coercion here.

It's a corporate governance problem because the relationship can be seen as tainting personnel decisions, even if it actually doesn't, but that's hardly a morality issue. It's HR optics.

Note that I'm not defending Huang, but I think he's done for because of the spy thing more than because of this.