MS's real issue is the 360 was the time when they should have been building up new devs and buying companies. They failed to do that and start of Xbone pissed away any good will they had with their number of fuck ups.
Phil Spencer did identify the issues XBOX faced. GamePass and BC was a good way to get back some of the good will they had lost, and he did start expanding the XBOX dev line up. However, most of the purchases didn't show fruit until 2023, three years into their next console line up, it was too late for it to dramatically change the fate of the XBox Series Consoles. Add to the fact, the first big game, Starfield, is now seen as a disappointment and after the first month will have moved all the consoles it was going to.
I've been expecting for years to see their GAAS output like Sea of Thieves make it to other platforms. I also thought the Switch could end up with smaller titles they published or some of their old back catalogue, but never thought it would go beyond that, like it seems to be going.
XBox Series consoles are selling like shit, and now with the purchase Activision, the heads of MS want to see growth and a return of investment in XBOX, only way they are going to get that is by publishing games on other systems. No way they could turn the Series sales around and with a more powerful Switch around the corner that will just make things worse.
But if they go all in of new games being multiplatform even if they come 1 year later, why would any one buy an XBOX console over a PlayStation? This is pretty much going to kill XBOX hardware unless they come up with something different. Like Switch, like a console with power in the ballpark of the next PlayStation or maybe a XBOX branded PC, that runs a more console-like version of Windows and also allows use of steam and other markets stores.