It’s ridiculous to suggest that compensation isn’t correlated with quality. There are many exceptions but it’s a good rule of thumb in the absence of additional information. It also just passes the sniff test - try comparing the Southwest Airlines app to the united airlines app.

I don’t think COLA matters all that much. The reason SV pays such high salaries reflects the underlying higher productivity of those engineers. The fact that much of that income goes to landlords in the Bay Area is orthogonal to the underlying quality of the engineers.