The key is that if you're above-average for a given market, you're average in a higher-valued market. All you need is a single job offer in that higher market

The key is that if you're above-average for a given market, you're average in a higher-valued market. All you need is a single job offer in that higher market to force your current employer's hand one way or the other. When you are the product on offer, the employer doesn't get to define what markets you're available to; they have to play the hand you deal. This applies geographically, as well - if an employer says "Well, they might be paying that rate in SV, but round here..." then you need to be applying for remote positions. They don't get to opt out of that market either.