Ah yes, the Deck vs. Switch debate. One offers performance and affordability, the other offers nostalgia at premium prices. Choose your fighter: the powerhouse or the Pokémon tax.
Considering the Steam Deck can run just about every console game ever made up to PS2 gen (and a good amount made after), I'd say they have the Switch 2 beat on nostalgia.
You can emulate almost any Nintendo game from before 2016 on a steamdeck. Just got to wait a few more years for the switch emulators to get efficient enough to run well on the steam deck!
I know I'm not the standard pokemon fan, but showdown still exists if you just like to battle. The in-game gameplay of pokemon has always been a little lackluster to me and I don't like VGC/doubles.
ROM hacks can be fun, and I have done some self imposed challenge runs. I can't see myself finishing any of the Prof oak challenges I did without emu speedup.