That's not what I said (although the salary differences between good and bad engineers are small, in comparison to the differences of output).

A good, senior engineer (10-15 years experience) is typically going to get $150k at a large company and drop to $110k at a startup. But it would take at least $75k/year in equity, for a savvy person, for that drop to be worth it. A stock that is correlated to your employer should be worth less to you than one at zero correlation. Moreover, it's an illiquid stock. Furthermore, VCs are buying preferred stock while you have the common kind, and that can easily be a factor of 2 (or 4, or 8+) of difference in fair value.