The difference in practice is nowhere near that though: I made those 60K when I graduated, in 2000! Salaries in the midwest for experienced engineers are far better than 80K: A few years ago, I made 120K as a full time employee in St Louis. A darned good house is 200K. Consulting gigs pay more: Last year I billed 220K, just a single customer.
In comparison, I know senior engineers in the bay area making 150K at companies you'd recognize, with stock packages that don't mean squat without liquidity events. And a SF house equivalent to the 200K St Louis house is 2M. They aren't getting a good deal.
It seems to me that the problem with your argument here is not that you aren't right, but that you are providing numbers so far away from reality that people can pick them apart and claim that the midwest is a bad deal. A 60K salary upgrade would make San Francisco appealing. But in practice, the range is far smaller, and that's without taking into account companies that hire remote.