Ownership of studios is definitely not compulsory to develop big AAA games. Say what you will of MS, but they definitely have found success with Playground Games and Remedy in the past for developing exclusives.
But third-party external AAA development is also something that I'm seeing to be more and more volatile in years as the investment and operating cost to make AAA games are ballooning.
I mean, I look at ReCore and while it's clearly not intended as a high-budget AAA game in the first place, it feels also very much a "bite off more than we can chew" game from Armature, who is a small 50-person dev team, where they've got the budget for it, but not necessarily the other resources to build what they envisioned.
From an outside-in-perspective, I look at Crackdown 3 and have that same worry to an extent. It's a three-studio collaboration in engine/tech/creative/development between Cloudgine, Reagant and Sumo Digital, and while we've definitely seen successful multi-studio collaborations before, it also feels like a necessity forced by the reality that the creative forces behind Crackdown at Reagant don't have the development resources to build Crackdown 3 on their own.
Also, from a forum gaming fan perspective, external development also limits our ability to predict and guess what's in the pipeline for MS. And let's be real, we all find entertainment in E3 guesswork, and external development only hinders the fun of guessing because it's boring to list down in prediction list something like :
- Unannounced AAA game from some external dev MS contracted