I think they're completely different audiences. Nintendo games aren't, and never were about cutting edge graphics or the latest tripple A games. They were always about family/kids oriented more casual games. Which is not to disparage them in any way. I like playing some nintendo games every now and then.

But my mom bought a Wii back in the days. For herself. My mom doesn't usually play video games. And she is most certainly not at all interested in playing Doom or Hades (just because they're shown prominently on the webpage). But she liked Wii Fit and bought a Wii.

I honstly think the subset of people who would buy a Steam Deck to avoid buying a switch is so small, it would not put a significant dent in nintendo's bottom line.