You haven’t talked about how much you care about portability and ease of assembly.
The only reasons to buy a Steam Deck is because you can use it on the go, and maybe because it already comes pre-built and pre-configured with an OS. So it would be interesting to know how important those two things are to you.
If they are not/not very important, then a Steam Deck makes no sense, as you can get the same power of hardware for much cheaper in a desktop.