A Series X will not render very many AAA games at 4k/120fps (if any at all). And it definitely won't do at Ultra level settings.
PC gaming at the high end has always been about spending a lot of money to get the best graphics possible. Consoles always have much better bang for the buck early in a new console generation.
The 4K 144hz you get on the Xbox Series X is almost certainly lower graphics settings than you could run at 4K 144hz on the RTX 4080. I don't think the difference is enough to justify the price difference but comparing resolution and framerates isn't apples to apples.
And you'll still be playing the same game. If you want to spend almost a thousand dollars so your game renders more eyelashes that's your choice. My point is that NVidia's pricing is making PC gaming inaccessible to people who don't have wads of disposable cash to spend on diminishing returns. I would strongly recommend anybody who's looking into getting into current gen gaming to steer clear of playing on PC as the pricing of PC components is completely out of control and console pricing is looking increasingly more reasonable.
How is it making PC gaming inaccessible? You don't need top of the line hardware to play even the most recent PC games. You need top of the line hardware for "more eyelashes", but that's very much a choice (that you get with PCs but not with consoles).
4K 120hz is merely the limit of the HDMI standard used on the Series X. It is not a hard requirement needed to publish on the platform. This would be akin to claiming that the PS3 was a 1080p 60Hz console, when the vast majority of the library managed closer to 720p 30hz.
While developers are free to make 4K 120hz their target, few games attempt it, and the ones that do, often make significant graphical compromises or are graphically undemanding to begin with.
correction: 120hz not 144hz.