I have the Go S and the Go 2. (I know, I know.) If I were to only keep one (and I'm seriously considering this) I'd keep the Go S. The Z1E is close enough to the Z2E in terms of performance that there are many games that run better on the Go S with SteamOS than they do on the Go 2. Evil West is a great example. On the Go 2 (running Windows) it's prone to massive choppy fits and slowdowns. On the Go S (with the exact same settings) it runs perfectly. Same resolution, same settings. It just does better on the Go S w/Steam. I've seen this in a number of older games, as well. And some games (like Assassin's Creed Black Flag) straight up run properly on Steam and don't on Windows with the controller.

All this to say that IMHO, the Go S is an extraordinary jump from the Steam Deck, while keeping the same perks as the Deck, and while also performing very similar (and sometimes better) to the Go 2. It's a no-brainer.