you're only doing this after you made your money in the USA and will presumably be far richer than your neighbors back in the EU.

His savings will be higher, sure (though living in SF is horribly expensive so he might not have as much as you think). However, his income in the EU will be the same as his peers there, and he'll need to live within that new income.

Having a lifestyle that costs more per-month than your income is stupid and unsustainable; it's unlikely he has that much money saved to live that way for the rest of his life. So, at best, he'll have a bunch of cash to pay for a nicer place to live if he decides to purchase something (and if so, he'll still have to pay higher taxes and living costs out of his current income).

Basically, he has a really nice retirement savings now. He's probably not going to be living like a king.

You could just move out of SF to like, Miami or Atlanta ¯\_(ツ)_/¯

I mean you do you, but you're really describing a problem that doesn't exist outside of SF, LA, and Seattle.

Or to Redmond/Bellevue/Kirkland/Issaquah (suburbs of Seattle).

Sure, come over the our EU utopia...

Come to think of it, if only it would be possible to do a swap. Half a mil a year to live in SF sounds harsh but worth the risk.