Good question. Ask the folks posting these videos of Switch emulation.Ok. How about other games?
Old Raspberry Pi3s can run Mario 64 at full speed but good luck managing Conker on the same emulators/settings.
Some games are easier to emulate than others. Some games may also be heavily targeted by the emulator authors, like how BOTW was the target for CEMU and the game played great, even though most others had all sorts of issues.
Look, i'm not saying the Deck isn't going to be able to do it but knowing about emulation, my expectations are low.