I love the steam deck. I haven't used my switch for anything other than family Mario kart since I got it. I really like having access to PC games, especially at steam sale prices, which makes the deck a lot cheaper in the long run vs Nintendo games that never go on sale. Even Pokémon games that are years old are still full price when they're 2 or 3 releases behind in the series.
The only thing I prefer about the switch is physical cartridges. The deck wins in every other category for me.
Battery life definitely depends on what you are playing. In BG3 I get around 2 ish hours. But I can play older games like Morrowind, or newer retro style games like Skald against the black priory (10/10, do recommend) for 6-8 hours, maybe more.
You also have a lot of control to improve battery life like clock speed, frame rate limiting, etc.
But yeah it has a huge screen and if you play newer games with good 3d graphics it drains fast. Switch doesn't really have those kinds of games so it's not a 1:1 comparison.
EDIT: I also agree with your points on it being very bulky and not well suited to a 10 minute session. Launching games is slower on the deck and most PC games have more loading screens before gameplay.