You've made a huge mistake by assuming that someone that pays for Office 365 email is using it only for work. Some of us use it for personal email.
I've used my personal email address for Microsoft account for many, many years, and a couple years ago I also subscribed to O365 for email. Logging in has been weird, but not because I had to choose an account type, but because the MSFT account insists on showing an outlook.com address for everything, which I wish I didn't have in the first place. I was trying to set my real email address as the primary address for MSFT account, but wasn't a choice. I decided to try removing and re-adding it, but now I cannot do that because the address is associated with my O365 subscription.
I really regret removing my personal, real email address from my MSFT account because I will not be checking the outlook.com email account and now I will miss any important emails.
Frankly this was the worst way to try to fix an existing problem, especially when some of us never considered it to be a problem in the first place.
Update: To further complicate things, I can't add *any* email address at the domain I use for my personal email. I know it will make me sound like one of those crazy guys that rants at the internet, but this is stupid. Incredibly frustrated.