The word for someone who performs a core company role in exchange for nothing but equity is "cofounder".
The word for someone who is paid to do work but who is responsible for all their own taxes is "contractor".
It freaks me out that the Appeals court decided that these factors weren't "dispositive" of the engineer's relationship with the company, because (pp) "that's how startups work". The hell it is. If you want people to work for you, you get an employment contract together. If they're employees, you pay them, and you do W2 withholding.