I mean, that is exactly what Google does. Google does allow the change you listed above, which is nice. But if you don't explicitly change your accounts, you keep getting the "pick an account" screen on every single login, just like the parent described, and just like Microsoft shows users too.
To clear up the confusion: Google has that UI, but it's legacy. They no longer allow you get your account into that state; new G Suite accounts and personal Google Accounts can't use the same address.
How legacy? Personally I made this change/split maybe 12-15 months ago and still get the prompt. I'm also pretty sure I had a client with this same issue recently, although I can't confirm with certainty. I routinely migrate clients TO G Suite which is why I have some first-hand exp here.
Also, when signing up the Google system will not allow you to use the same email (if it's registered) but once you "take over" or verify domain ownership, you can then claim / use that address - which I believe creates this situation.
I mean, that is exactly what Google does. Google does allow the change you listed above, which is nice. But if you don't explicitly change your accounts, you keep getting the "pick an account" screen on every single login, just like the parent described, and just like Microsoft shows users too.
Google's UI for it looks like this : https://lh3.googleusercontent.com/-_g4V2wYd-SI/VrZF-5K2yCI/A...
Which is very similar to Microsoft's UI for it : https://docs.microsoft.com/en-us/azure/active-directory/medi...