I’m trying to defend here a product I don’t really believe in, so bear with me.
The portal lets you play PS5 games, in PS5-ish quality (-ish because it’s obviously not the same as a 4k TV). The best the switch can do is 7-year-old No Man’s Sky, with no multiplayer. Recent Pokémon and Zelda (first party Nintendo games) can’t even reach a constant 30 FPS in the whole of the game.
I don’t think graphics are THAT important, but I know there are people who think that. And in that case, the PS5+Portal is going to beat a standalone steam deck or a switch. If you have a beefy PC maybe a steam deck can stream in better quality, but if you’re in the PS5 ecosystem it’s the best quality handheld gaming you can achieve.
Would I buy it? Absolutely not. 80% of the fun with my steam deck is taking it places. The airport, the plane, a hotel on a business trip, my partner’s place, the dentist waiting room, the bus/train… All that’s missing with the Portal, but that doesn’t mean I can’t see a (niche) market for it.