I recently acquired both devices and most of my time is probably spent playing the NS2. I do love the Deck though, it's basically reignited gaming for me. It's not perfect as some of my main games are Train Simulator and I like others like RTS games, which don't tend to work well on the Steam Deck. What I have started doing though, is playing my older games that I never touched while sitting at my main PC. Even the LCD screen looks great if you can get that a little cheaper.
If you value Nintendo's first part games, definitely go for a Switch 2 but just know that the cost will only increase as you buy more and more. You already have a decent library on Steam, so as long as the type of games you play on Steam are good on the Steam Deck, it's the much cheaper option.
I've had a desktop PC for years, yet I spent more than 90% of my time gaming handheld as it's just more convenient. If you aren't in a hurry to buy one or the other, wait and see what the Steam Machine will offer.