"MAKING THE BEST PLATFORM":
w.r.t the platform, I understand your reasoning, but I don't think that always works, otherwise Windows Phone would have done better. I recall MS offering incentives to devs to create the apps, but without the users few devs could bother. Without the apps few users could bother switching. Likewise, I think without the content the users won't come, and without the users few devs would be arsed to port games over. I think Good Old Games offers something amazing (games, particularly old, without DMA) and it's quite niche.
Not sure about Epic or Steam, tbh. Please can you explain more about these? Steam was something I saw as windows-specific, but they also have their own steam deck stuff.
"10 YEAR PROMISES":
I understand what you are saying and I agree Microsoft can't be trusted, but the 10-year promises are something they thought would satisfy the market authorities because of Sony's concerns. I also think Balmer-era MS is different to Nadella's, as we can see from the way MS has reacted to Open-Source. I don't believe this is any charity from their side, but a business decision for increasing profit/reach/influence, but I can't imagine .NET core would be a thing under Balmer's influence.
Degradation on other platforms
Yes, this is a concern, and I don't know what the solution is. But as we are talking about Cloud platforms the only concerns are bugs, lack of DLC, and difference in cost on other platforms, assuming they are still forced to offer their games on other platforms. However, I still cannot see Microsoft these days employing the same practices they did before---especially since they're not as loved as before and won't be able to get away with mich.
Activision Blizzard
I dunno. Perhaps I'm not really into gaming as much as when I was in my teens, but this company has come under so much bad press that I don't think they're all that important as they once were. I don't think it would be good for gamers but only because I think, like in the past, Microsoft gobbling up a company kills it off. AVB would essentially just end up producing terrible knock-offs of its own IP, giving the opportunity for another company to take the place it once had. Microsoft taking AVB under its own wings and smothering it can only be good.