Microsoft and Xbox Accounts = Godawful Mess

I signed up for XBL on my brothers xbox ages ago, with my standard email. Then much later when I got my own xbox I signed up with my secondary email. Now some years hence I am having significant problems with Win8 because of the way Microsoft Accounts work. My user login was my standard email of course, but then games were associated with my brothers Xbox account. No big deal, but then my brother needed better access to his XBL, so I went and changed some settings, and it turns out that the Xbox account was secretly a Microsoft account. Now if I put his email as primary I log in to windows under that. So what happens when he sets up a win8 computer, will he get all my setting and I get his?

Microsoft's solution? Create a new user. This is unacceptable. Get your act together MS and get yourself set up to deal with this problem in a mature way that shows you can handle cloud and some basic realistic issues that come with it.