Wouldn't that still be one auth service that looks at one of two db tables though?
I didn't really see it coming because I didn't even realize there were Microsoft accounts until shortly before the migration. When I was then forced to migrate I found out that I apparently alrealready had a Microsoft account that I luckily had the password written down for, all in all a horrible experience in my opinion.
Also the fact that you need to mod the game to avoid telemetry nowadays is just sad.