Having been in this exact position multiple times now (once quite successful, others not), you should probably consider it a wash.

Unless the company hits unicorn AND your shares become liquid (secondaries don't count—you generally won't be able to sell enough shares to make a meaningful dent), you'd make just as much or more at a FAANG firm with way less risk.

Of course, I say this while not at a FAANG firm, because I prefer startup type work.