This is weird. Software going down yoy is not a great indicator at this stage and you can't "blame Fortnite" and shrug it off as insignificant. I suspect the focus on game pass is eroding the amount of money spent on software and that's a problem they'll have to solve going forward.
I'll go out on a limb and say that if this is actually something MS considers a problem internally. Then they either already have a plan for how to deal with it, or currently have a bunch of highly skilled people looking at how to fix it.
I personally find it weird that people on era seem so doom and gloom about xbox, especially since MS have actually, for probably the first time since they got into console gaming, started behaving in a way that makes seem like they have a solid vision for the future of xbox
Honestly if anything. I'd be more worried about Playstation in a world where all the big US tech titans like MS, Google, and Amazon, are focusing on gaming