The dev in Eastern Europe may do well to be reminded that the dev in SF is losing almost all of that on costs of living, and may actually be worse off in terms of disposable income (relative to its purchasing power in the area).

That might be true for someone that spends most of their income, but if you're attempting to save (to FIRE or something else), you'd be much better off in SF, since your post COL-adjusted take home is still significantly better.

10 years of working in SF and saving frugally, and you can go to the aforementioned places in Eastern Europe to retire for life. The engineer in Eastern Europe cannot do the same.