It won't hurt the switch, it never meant to anyways. It will and has however hurt it's fanatics! Anywhere i go i see them reassuring themselves or bashing the thing. It's funny.

Atari Lynx, Gamegear, PSP, Vita didn't hurt Nintendo and all of them were far superior when it comes to hardware, compared to Nintendo's counterparts. Besides the Switch is over 4 years old at this point. Even if the Steam Deck is wildly successful, it might be just enough for Nintendo to release a successor to Switch earlier or do the price cut of their current consoles. Either way, the consumer wins.

While I agree the current gen switch will not see a massive hit from the deck, I can only wonder how a future next gen switch will do, a switch 2 if you will.

What the deck has done is set a new baseline for handheld and if it "does" prove successfull, then nintendo will have to try and one up valve or I can see a bunch of people saying
"Well, why would I buy a switch 2, I already have a steamdeck" which, by the time the switch 2 launches will be cheaper

It will hurt neither

There isn't even enough Steam Deck to fulfill its own demand, seems like their manufacturing potential is small. People who are pre-ordering this week will only take their consoles in Q2

SteamDeck hurt the godfather of handhelds? I think not.

Honestly don't see it selling. Who wants one? Steam and pc gaming is mouse and keyboard, not small screen joypad. I don't know what gabe was thinking honestly.

I will buy one Steam Deck ( I was looking for a GPD Win 3 or Aya Neo before), but Nintendo Switch is not only a handheld console, it´s a hybrid system with only the base console purchased. The 3 ways of play, the indie market, and Nintendo IP are the pillars of the Nintendo machine. Steam Deck needs some adjustment for good competition ( a dock, more storage, and one detachable controller).

It´s more a niche product when you compare it to the Nintendo system. Some games to work need Windows OS for working. So the steam library does not work 100% before the launching. 

Me

I want one. But uses the wait and see approach after the launch. 

It won't effect Switch sales one bit. The hype will die down soon. The first units aren't out until December and waiting lists are already to Q4 2022. Meanwhile the Switch is available to buy. The Switch also just works. Steam Deck has a lot of possibilities, but most people just want to pop in / download a game and go, without looking at specs, tweaks, mods, compatibility with controls etc. Whether Steam Deck can offer that experience is the big question. For enthusiasts it's a great device, yet convenience is what counts in the end.

What effects Switch sales is not having a standalone option. I would buy a console version in a heartbeat.