What other option would hit their power envelope and product requirements? The only "newer" option is a smaller node of what they've got, which in reality would have given a slightly better battery life and marginal increase in possible clock speeds, at a much higher cost. Add it up.
Basically I don't think you understand how product design works.
Isn't the X2 pretty old news by this point too? Xavier is the new one right? Does Nvidia just not have anything better for mobile since 2015? Would be a bit odd. Must have been a REALLY good deal on those X1's. Dumpster diving NVidia does it again!
If the Switch had come out at £199 or something, yup you'd be correct and it's a good pelt 720p handheld the kids can kick around and it does portable Zelda. Good enough!
But the feature creep and bad production in other areas at £280 just makes the package look poor, especially in the hyrbid space it wants to occupy. Realistically HD rumble and all the JoyCon fartery is never going to offer more than a slight spec bump would have for the handheld. Zelda wheezing on launch day is a terrible look for brand new exciting hardware you're looking at maybe half a decade with.
The dock having absolutely fuck all in it, not even felt, when "they got a good deal on X1's" is one of those situations where I'm not sure Nintendo is passing on any savings whatsoever.