I'm sure a lot of this is familiarity, and if I force myself I will get more efficient with the Steam Deck, but I doubt I'd ever find it superior or even equivalent to keyboard and mouse.
The touch controls on the Steam Controller are excellent though, so I'm not sure how good it will be on the Switch which uses joysticks...
Whilst lots of games ignore it, the Switch screen is a touchscreen.
Regarding the ecosystem, the Steam Deck is a x86 PC. It comes with SteamOS, which is an open Arch Linux based distribution. You are free to install other operating systems like Windows on it. The out of the box Steam experience is quite good, with lots of games on the Verified list[0], and they play really well. People also install non-Steam games and software, including console emulators, and there are growing communities around that.
Elden Ring plays well. I don't plan on using my switch OLED until the next Zelda comes out.
I hope the Controller support been improved with this launch as I tried to play Factorio on my Steam Deck before but felt like it was just "emulated mouse" support basically which isn't nearly nice enough. I feel like Tropico-series did a good implementation of top-down+strategy controller for their games.
From the link:
Factorio was developed for 10 years with only keyboard and mouse in mind, so making sure the game is fully playable with controllers was no easy task. Playing with a controller is slightly slower, and will take some getting used to (just as it does when playing with keyboard and mouse for the first time). After becoming familiar with it, I find it very comfortable. I recommend everyone to play through the first levels of our tutorial campaign, as it's a great way to get acquainted with playing Factorio with a controller.