You are way off. I would estimate $100-200k for 4 years for someone with around 4 years experience when they join. This is based on some quick googling, glassdoor, quora and knowing that 600k+ stock for 4 years at established company for relatively junior positions doesn't make economic sense.

Acquihires and very rare skill holders or more senior roles? Higher -- if your friends of either of these, then maybe.