This is what I've argued with people in this very thread who insist that the Microsoft 1st party isn't going to be much different next gen because they only "bought Indies"....or "look what those studios did in the last few years".
Don't get hung up with the name on the front of the door. Many of the big time publishers have bought small to medium sized studios and expanded them into AAA game producing teams. Microsoft has some of the best creative leads in the industry as a result of their Indie studio buying spree. Outside of Double Fine and Compulsion, they've been expanding considerably. That's in addition to contract work which is heavy in states like Cali. Microsoft 1st party will have more games in development with AAA production values than any other publisher in the industry. Can follow LinkedIn for the evidence.
The main aspect to be aware of is not acquisitions, but rather organic growth. The studios under the XGS umbrella have grown tremendously over the past 12 to 18 months and it speaks volumes to the investment the Xbox division is making towards internal game development.
I don’t have exact figures but in doing a little research the growth across Xbox Game Studios looks to be in the 750-850 employee range (depending on how you break it down). That factors in the expansion of major studios like Playground Games, Obsidian, and Rare along with the continued build out of The Initiative in Santa Monica.