P.s. Your "about" checks out!
Now, I don't know if San Francisco has a bloated, runaway budget or not – it might! But I do at least know that it's both a city and a county; I expect that San Francisco's budget includes operating the ports and public hospitals – that could be $5bn in spending right there!
Endless time is wasted by not even doing the most basic thinking before spouting off.
Also, California has realigned a number of what were previously (and are still in other states) state functions to counties, including some felony incarceration that would otherwise be in state prisons, so, even compared to out-of-state city and county combined functions, SF has more it is required to do.
It's a good metric for a tax base.
> unless you think an $8 Big Mac is twice as productive to the economy than a $4 Big Mac
Which is why we consider both nominal and real GDP. (In your example, the former represents 2x nominal GDP. They're equivalent in terms of real GDP.)
It literally straightforwardly is. It provides the same number of calories, to a worker who is twice as productive in the $8-per-big-Mac city as the $4-per-Big-Mac city. Differences in per-capita productivity between supercities and hinterlands are vast.
Seattle's population is around 755,000. 755,000 / 2,400,000 ≈ 0.315. 10,200,000,000 * 0.315 = 3,213,000,000.
3.2 billion + 8.3 billion = 11.5 billion.
15 billion (San Francisco budget) - 11.5 billion (Seattle budget) = 3.5 billion.
So San Francisco's budget is around 3.5 billion dollars higher.
[1] - https://kingcounty.gov/en/dept/executive/governance-leadersh...
Also, sound transit provides much transportation services in Seattle, but it is not part of city of Seattle. On the other hand, SFMTA is a department of city and county of San Francisco.
How do you draw the conclusion you like to draw if you miss these?