It's also true that it's much easier to change jobs there. That's IMHO the biggest asset and what I used to argue for moving (wife won out).
The culture stuff isn't as interesting. Sadly, wife and I are just homebodies. When we were first married, we lived within a short subway ride of Manhattan yet rarely made it down there. We tend to enjoy cooking, reading, hobbies, etc. Kids are the same. Also, there are multiple other extenuating circumstances that make a move not possible at present.
I do agree with you about the opportunity cost of working outside high COL areas, and I agree that it's not a good thing. It's increasing the country's polarization, which bodes poorly for everyone. But you're right that it's the current reality.
What about my assertion about senior software engineers usually getting shuffled into engineer positions. Do you think that's true, or no?