Well,for one Vita is under-powered for some systems (like SNES). It has very good PlayStation 1 emulation performance though, thanks to its awesome PopStation emulator (proprietary emulator develop for Sony for PSP, that also runs on Vita thanks to backwards compatibility).

Switch is much better of course, however only the old non-Mariko units can be jailbroken without modchips, and while I do like the hybrid design of Switch, I still think Switch as a handheld is bigger and heavier than I want for a portable console. This would be solved with Switch Lite, but all Switch Lites are Mariko.

I quite like my RG350 to play old games (playing Final Fantasy VI right now), so much that my Switch is on its case for quite some time.