The hiring decision at Microsoft is made by the "As-App" (As Appropriate). This is normally, but not always, your last interview, and while overall data points are considered, As-Apps frequently veto or hire independently of the overall data, and make the hire decision solely based on their own impressions. There is also not always a debrief - this is the exception, not the rule. Normally, the hiring manager speaks with the AA, and they decide. Not saying this is right, wrong or indifferent - this is just the Microsoft process, and it works well for Microsoft.