YC could use their leverage to do so, if they were so inclined. The only other option is for tech employees not to take jobs at firms with less-than-ideal equity terms.

Employees have plenty of rights, you're talking about giving them additional privileges. No one forces people to take equity compensation instead of salary and as long as employees continue to do so the practice will continue.

I don't believe equity should be instead of salary but if you are given the option of owning what you create, you shouldn't be enslaved by it.

It's horribly insensitive to even mention slavery in the same breath. There are actual slaves in the world and this is a completely different situation.