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An important distinction is that these companies generally do not and have not ever described location-based pay differential as cost-of-living. They are pretty consistent in saying that the differential is due to hiring market competitiveness. If they choose to hire in a particular market (because they have an office there), how much does it cost to make sure they get the people they want in that market?

This is somewhat but not entirely aligned with cost of living, and there have always been clear examples of better and worse markets - eg engineers in London are not that well compensated compared to their cost of living.

The big losers here will be people who lived in a HCOL location and yet still had a long commute to an office. They have no tradeoff to leverage if they decide to leave the high-pay salary market.