When it comes to consistently providing content for a subscription based service that's trying to get it's hooks in customers that's not going to be enough. If they were only focused on the traditional business model only it would be.
Even beyond that Microsoft has the issue of bleeding talent. They buy a company and the talent leaves gradually over time and either the company gets shut down or becomes a shell of it's former self. They're a lot like EA in that they cannibalize companies to continue their existence.
They have a real culture problem of seeming like everything is just a business transaction. When the Todd Howards and Tim Schafers inevitably leave who they gonna be left with? I genuinely think the developers at Sony and Nintendo are passionate to be there long term and see value in staying on. I genuinely think the developers at Microsoft are just collecting a check for a while and will end up leaving to do something they're actually passionate about.
There is a level of desperation at Sony and Nintendo that Microsoft will never relate to. For those two gaming has to work or it could damn well sink the company. Gaming will never be that important to Microsoft.
In fairness, the bolded is less a Microsoft specific problem, and more of a corporate problem as a whole. The age of the AcquiHire is behind us, so really, these acquisitions are now primarily more about IP. These companies go into the acquisition knowing they're going to lose people through a variety of (self-created) redundancies, hurt feelings over org chart changes (or lack thereof), and people just wanting to work elsewhere, or do different work.
And ultimately, talent shifts around a lot in the industry, so it appears Microsoft's ultimate goal with some of their bigger gaming purchases is less about getting top talent directly, but more about getting access to properties and studio names that they think will attract talent to them.
That said, you are right that gaming will likely never be as important to Microsoft as it is to Sony or Nintendo. But while the gaming division has been the most consistent part of the company for Sony, I don't think it'd be a wrap for them if that part of the company somehow went over.