Xbox users buy plenty of games, otherwise publishers would stop releasing games on the platform.
I think at least some of those publishers are only bothering with their games on Xbox because Microsoft is footing the bill for porting costs and the such. SEGA & Atlus are two prime examples. Some of the Square-Enix ports as well.
Basically, a decent number of Japanese ports are working this way.
Not sure if it's in best selling order, but UK has it 1st, 3rd and 7th.
IMO the game's going to do better than some want to think. It may not be everyone's cup of tea, but it is kind of unique among GAAS titles on the market so it stands out in that respect.
I can see probably doing 2-3 million in the first month or two. Also don't think lifetime of 10 million is out of the question but that would be several years from release. The game'll probably also get a Switch 2 port which will help a lot in getting more sales (though will be somewhat hamstrung by Switch 2 needing to grow its install base releasing 4+ years after PS5).
If anything, the Xbox diehards who want MS to double-down on the console should want this and the other ports to fail, not brag when preorders and sales on other platforms are high. But they hilariously can't do that because it'd mean wishing badly for a Microsoft game. It's like the hidden 4th prime directive in Robocop.