well, switch 2 has the best shot to be closer from the other 2 visually since the GC. They are focusing in achieve 4k as standard(they could improve far more I visuals if the standard was 1080, but it not seems to be the case), so, seems they wont push the maximum of visuals/effects as they could. So I cant see a lot of improvements in visuals compared to ps4 and one, just a native 4k version. If switch 2 is well designed, come in the right time(2023/2024), and new technology, it can run all ps5/scarlet games on handheld mode. yet not in 4k, 720 to 1080, but all playable on HH mode.
Well, on dock, otherwise, they could use the technology NVIDIA is starting with RTX, use DLSS to increase the resolution post rendering to until 4k to deliver almost the same visual fidelity when compared to other versions of the game. The DLSS dock will not be cheap, however, but they may offer 2 SKU at launch, one with a simple mini dock (that just streams) and other with DLSS. id go with 250$ and 400$, 2024.