Every login will prompt to select the organizational account, or the personal account.
Not sure why only MS is being called out for it ... they probably modeled their system after Google.
Unfortunately you cannot merge. Google services will have an option to switch between the different accounts. The priority order is shared, and to change the order you have to log out of all your accounts and log in again, with the primary account first. I decided to keep my @gmail.com account first, so I only have to switch to the @example.com account when I check GMail.
Could be much better, of course. I was personally a bit frustrated with the process.
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...
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.
Then, an admin who proves they control the entire example.org domain registers it for G Suite, and creates a 'crb' user.
You now have a conflict account situation: https://support.google.com/a/answer/7062710?hl=en
I occasionally have to perform some bizarre incantation once in a blue moon to switch accounts when I want to comment on something and then switch back so I can see my subscriptions again.