No way can a PS3/360 run Tears of the Kingdom at 60 or games like Diablo III at 4K ... the Switch can, it's basically proven on video. The chip is way beyond a PS3/360/Wii U IMO.
Nintendo just wants people to pay up more $$$ to buy a Switch 2 to get those features IMO (same reason they also won't give people GameCube/Wii games on Switch Online ... they are going to force people to buy a Switch 2 for that even though there's no reason a Switch 1 can't do it). Which is probably business wise the correct call (I would do the same thing if I was Nintendo president, matching Switch 1 sales will be tough enough as is without a COVID surge in sales for 2 years, having Switch 1 models that could do 4K would just make trying to sell a Switch 2 upgrade more of a headache).
Unfortunately I don't think we'll ever know what the max the Tegra X1, especially the one inside Mariko and OLED models can do. Another casualty of COVID basically creating a weird time line. If COVID doesn't happen then I think the Switch has a more regular sales curve where sales start to diminish by year 4/5 and Nintendo pulls the trigger on a proper Switch Pro/4K which they just borked into the Switch OLED instead.