Nintendo has the best 1st party games. They care a lot about making games that are just fun. What does Valve have? Lootbox, gambling ridden, addictive dopamine juicers. Their offering sucks compared to Nintendo.
Portal and Half-life series will forever be some of my all-time favorite games, but yeah their newer stuff does seem to be not that great, though I'm very much a "play local" kind of guy
No one is gaming on PC because of "first party" games, and Valve's offerings are literally the whole of Steam with more excellent games you could ever possibly play in a lifetime. Then there's GOG and the other stores. Hell, there are many great games outside any of the major stores. This flimsy excuse only has any sway if all you want to play is the next Mario or Zelda slop, but even then there are emulators.