>Higher incomes have historically been a symptom of productivity

If I go to Zürich I get a burger for 30Fr that I can get in Southern Germany for 15€ and in Berlin for 8€. That is with roughly the same quality.

I'd say past productivity leads to network effects and investments in one area that boost local salaries and decouples them quite strongly from current productivity.

My previous company had a per-dollar extremely unproductive location in silicon valley. The people there weren't at fault. You don't magically become more productive because you live next to SF.