It is actually pretty fine for steam deck. It’s has to be a console like experience.
For a desktop os? not so much
Well on my SteamDeck I wanted to install Portmaster for Adblocking and network filtering, and also wine because running Windows apps with a click on the Desktop > Opening Bottles and setting each one up before, Also wanted to switch KDE for Gnome because KDE sucks on a touch screen big time where Gnome is much more touch friendly. Also wanted to install neofetch as well but just ran it as a script to get what I needed. Yes I can disable the read-only and do it all anyway, it’s not really locked down but because SteamOS doesn’t respect or honor changes they’ll just undo it whenever I update.
To be fair you are trying to use steam deck for what it was not meant to do. You are an edge case. The os was built for steam + flatpack, for games.
It works for that. To use it as desktop os… See my comment above :D
It’s a computer and he is a linux user, nothing is stopping him. Also, you can use distrobox to run applications in containers