M$ is a 2.5 trilion dollar company that can't manage game studios because it's not one of their core competencies. They prop up their failed xbox gaming division with enterprise sales and cloud computing. I honestly don't think M$ even cares about xbox as a console; it's just a vehicle for cloud gaming, subscriptions, and a way to ensure developers also develop for PC/Windows.
M$ is looking long term. They can afford to bleed money for another 5 to 10 years, as long as they buy brands/studios with influence; they'll try to condition the next generation of kids to accept subscriptions and live-service games. It's the worst of worlds; a regular gaming company would be forced to innovate, restructure, or sell itself--xbox can just fail and instead of improving internally, they have unlimited non-xbox money to spend.
I also think xbox, even failing, is just a marketing vehicle for M$. They want to influence kids and teens into associating M$ with cool things. They've failed to produce any games (yet) to compete with Sony this generation, so their last ditch effort is to just buy a studio with mindshare. You'll never hear a straight answer as to how much money xbox is losing, because they probably hide it behind some cloud/services or marketing account.
There is one way I'd be okay with M$ buying Activision Blizzard: they need to spin off the xbox brand into it's own company and let it stand on its own. Then, we'll see if the company is really viable as its own entity or if its just a money-losing strategic brand for M$.
But I do love how you start with the big problem: Microsoft has not bought studio and enhanced them as studios or companies. Look at what Rare has become.
I don't trust Microsoft owning companies, but I don't think them buying Activision would be a good thing for anyone but Microsoft. Ultimately Microsoft is only interested in Microsoft and the people supporting the merger to get Activision on Game Pass will turn around and whine when they increase the price after the merger is clear. Everyone on that side is self serving as fuck.