It's also really ethically dubious to sleep with someone you have that kind of authority over

Why? It’s how the mammal world works since the beginning of time. Females seek out the alpha male.

"Is-Ought Fallacy" is the right search term.

The "alpha male" is not even how wolf packs work in the wild: https://www.scientificamerican.com/article/is-the-alpha-wolf...

The researchers who coined the phrase eventually realized it only applied to artificial packs in captivity, not the wild.

Mammal world has also worked by killing another mammal with food you want if slightly hungry. Yet, for some reason, people don't question why murder is illegal whenever someone gets convicted of homicide. Selective appeals to evolutionary history are an empty argument.

It's certainly an abuse of power and a lot of companies in the US forbid this explicitly, often in employee guidebook

That's where the "disclosure and reassignments" come into play - you can date a direct report, as long as you let the company know they should report to someone else from now on.