You nailed it. The people with big salaries are fleeing.
The big urban areas will shrink faster than most people expect. The majority of those white collar jobs only exist to provide a service to someone in the financial industry. Developers are kicking office days to the curb. Who wants to live somewhere that make you fantasize all year about getting away from it for a couple weeks? Why not live someplace you love in the first place?
Those jobs are leaving the area and they're paying their taxes to the place where they live, so it's a win for most of them since those cities and surrounding areas have ruinous tax rates. Fewer people disposing of big cash in a city or paying its taxes spell's that city's doom.
We're seeing a tipping point in civilization.
Good observations. It's not just finance of course, but all "white collar" type jobs that big cities have as their advantage. I've wondered about this too for some time. On one hand like you say, it's more possible then ever to have decentralized networks, and people are starting to see that the costs and negatives of living in a mega city are really high. On the other, the historical trend has been for increased urbanization for the last 500 years. Most of that really is because of improved transportation and technology that enabled fewer people to produce ever increasing amounts of agricultural output. Then there are entrenched interests of wealth in big cities who don't want those places to loose relevance or power: those in power there have a collected interest in keeping NYC functioning and real estate prices climbing since they are part of that network. Which CEO there would want to move those jobs to remote and then have to go vacation with all his friends in the Hamptons and hear about how he's destroying their mutual interests?
But it appears we're reaching the end of the number of people out in the countryside who can move into urban areas--at least in developed economies. So maybe now with more remote work people will keep their "city jobs" and move out to smaller towns? Lack of jobs has always been the big disadvantage these livable communities have compared to the large cities. It will be interesting to see how this plays out.
I've struggled with making a prediction as to which of these factors will dominate, and I could see it go either way. I'm also pretty aware of my own ideological and personal beliefs that might skew my thinking on this to wishful predictioins. Personally I think the more healthy outcome for society would be increased decentralization and move away from these mega cities and centralized institutions.