You'd be better off comparing the Steam Deck to products like the OneXPlayer and GPD Win Max, which are effectively portable gaming computers. The Steam Deck is a lot cheaper than those products, but also uses an older CPU while the others use newer tech. The 2021 GPD Win Max even has external GPU docking if you buy one of the Intel models. It's form factor is also more like a mini laptop, while the OneXPlayer is more like the Steam Deck. You also get more storage options and better battery life.
Basically, the Steam Deck has a good price point but limited expandability.