It isn't that simple - investments and their returns have risks built in, and people expect more return for more risk. If you are an employee, you are not risking your own money, you are just losing some opportunities for cash. This lost opportunity does work into the equation, but not at the same risk level as an investor because if the company tanks, the investors lose every dime... But the employee still got paid the whole time.
I do agree that for negotiation purposes, considering pay below market value is a good point for discussion. But don't get offended if it is not weighted as heavily as people who actually wrote checks.
> if the company tanks, the investors lose every dime
If you choose a $90k job + equity over a $130k job, and the company tanks 2 years later, you've lost every dime of that 80k.
It's a bit different since your "investment" consists of 24 tranches, but that's more than balanced by the vesting schedule which gives you nothing for a year (despite accepting your investment immediately), and takes it all away if you stop investing.
Actually, as an employee, you're actually risking more, as your total wealth is (most likely) significantly less than an investor's, so according to the economic theory of diminishing marginal utility of income, $10k/year is a significantly greater loss for an employee.
I do agree that for negotiation purposes, considering pay below market value is a good point for discussion. But don't get offended if it is not weighted as heavily as people who actually wrote checks.