> Meanwhile, a 20-something engineer at a six-figure salary can tell you how much of that they get to keep. (hint about half here in California)

This is patently false. Before even counting any deductions a married couple with a joint income of $300k in CA pays an effective income tax rate (Fed,State,Local) of 29%. Single at the same income pay 38%.

Once you add 401k contributions and the variety of pretax spending benefits, it goes even lower.

Go ahead and model it:

https://smartasset.com/taxes/california-tax-calculator

You have to be earning $3 million a year before you hit an effective tax rate of 50%.

People making that kind of money and more in SV aren't usually making it via regular income but rather via tax minimizing deferred compensation plans taxed at much lower rates.