It does seem like a big gap, but the docked target resolution is 4x the handheld target resolution, vs the 2x of the Switch. DLSS muddies this a great deal since they could just rely more on upscaling when docked, but the resolution gap could be good motivation.
Its 4x as many pixels to use every pixel on the screen. I'm not sure it's 4x as many pixels to looks "basically as good as it does in my hand."
Just thinking out loud here - one way to think of it would be, if you suddenly had an 8k TV, just as far away from you as your current TV, at the same size of your current TV, would you want docked to be 8x as powerful?
I think you'd probably say "rendering at 8k is a waste, give me a prettier 4k image instead." So let's try asking a different question - is there a resolution that looks "as good" on the TV as the 1080p screen looks in my hand? Extra resolution might improve quality, or not, but really, what's the line where the experience is about the same.
There is no hard and fast answer to that question, but here is one way to look at it. The further back from an object, the smaller it looks. I hold my Switch about a foot from my face, the Switch 2 screen is 8 inches diagonal, roughly, and 1080p. We can compute, roughly, how "big" a pixel on that screen looks in my view.
My TV is about 6.5 feet away from my couch, and it's 50 inches. At what resolution is a pixel on that screen as big as the pixel on my Switch? Well, this is a little outside my area, but there are calculators exactly for this, it's a common enough problem in graphic design, especially for large posters and the like, at far distances.
The resolution is... actually 1080p at that distance, believe it or not. But that's for static detail, our eye tends to pick up more information when an object is moving, blurry and fuzziness get worse. So let's be generous and call it 1440p.
For games to have about the same image quality on my big screen TV as on a handheld, you only need about 1440p res. Higher res will improve quality of course, but that's why devs so often don't hit 4k on even the PS5. There are other ways to improve the quality of an image (depth of field, anti aliasing, anisotropic filtering, ray tracing) than resolution -
better ways for certain kinds of games and content.
Devs will make the same kinds of compromises on Switch 2
no matter how much power you deliver. If the gap between the handheld and the docked configuration is too large, then when games
can't hit full 4k on TV, they might have decent res there, with great effects, but cutting it down by 1/4 for the handheld will result in a spectacularly bad image.
Inevitably games will look like shite on the device. I think Nintendo will opt for a configuration that helps ensure that games that look like shite
stay that way whether or not it's handheld, and games that look good stay looking good in both modes.