I'm tempted to think that the impact on the tax base is the larger piece here, since wealth at some point doesn't contribute that much more to local businesses (e.g., I think the number of people is more relevant for business impacts, whereas the income is more relevant to taxation).

I'm also not sure how this accounts for changes in income, as in maybe the people leaving are simply more senior than those coming in, amd this could be a normalish situation? E.g., if there's some normal increase in income levels of people staying in the city and then some portion of very well compensated people leaving, there could be an equilibrium.

The missing piece then is the change in income for people that didn't move.