The steam deck doesn't come with a dock, has a worse screen at 800p/60Hz compared to the S2's 1080p/120Hz, is way larger and thicker, doesn't have detachable controllers so if you do buy the dock you'll have to bring your own controller. It also can't play in a kickstand mode which is a negative if you're wanting to play with friends outside which is something I do often with my Switch 1.

I like the Steam Deck, really, but it's not a 1:1 comparison and I think the average person will still really prefer the Switch 2.