The Deck’s power management features are a solid selling point. There’s no reason they couldn’t be implemented elsewhere, and it would be a boon for other portable devices for sure.
I haven’t used the Ally, but the Deck’s touchpads are just intuitive and functional, it seems so obvious in hindsight that it’s actually shocking that nobody had thought to put them on a portable until now. They work great for replacing a mouse in mouse-focused games, and for navigating desktop mode. Much more effective than navigating with a joystick.
The Steam Deck is sold specifically as a gaming handheld. If you’re buying it to read PDFs, you’re buying the wrong device. Besides, the resolution isn’t the issue for reading documents, it’s the size of the screen. If you want to do non-gaming things, you’ll be much better served if you plug in a monitor, in which case you can even use a 4K display if that’s what you want.
I think the SD does have its issues, but I feel like the display is not one of them. At that size, it’s a good resolution to get better performance in games. A higher resolution would kill the battery, reduce performance, and due to its size it would be hard to tell the difference in-game.