I don't really know what should be done about salaries. I don't really believe that "fairness" can be defined, or even if it could be, that you could get a global workforce to agree on a definition.

On the other hand, I'd take the opposition position of yours and say that we should be incentivizing people to live in big cities for [many reasons](https://www.city-journal.org/html/why-big-cities-matter-more...). It is not perfect or tradeoff-free, but nothing ever is.