The deck shines with its default OS, and while installing other OSs is possible, it’s probably not gonna be a great time. Though you may not need to, as the deck’s desktop mode is pretty capable for light browsing/working. Especially now with the addition of the nix package manager.
As for the dock stuff, you’re not wrong, but a dongle would work just well as a dock, so if you want to wall mount it, you just need to leave enough space to hang a dongle to it.
Overall, a beelink would probably work best, and give you fewer headaches if a desktop is what you’re looking for, but the deck has the portability/handheld factor. It’s really gonna be up to your needs, which one is better.