This is straight up false. SteamOS is not limited to playing games distributed on Steam. It's a Desktop PC running an optimized interface by default. You are a

This is straight up false. SteamOS is not limited to playing games distributed on Steam. It's a Desktop PC running an optimized interface by default. You are always just three button presses away from launching Desktop Mode and installing whatever you want, as long as its either made for Linux or runs using a compatibility layer. I'd even argue that a device like the Steam Deck, with its open approach in almost every design choice, is a counterexample for "dumbed down devices". It has an easy-to-use UI for people who don't want to fiddle around with it, sure. But as even its operating system is, for the most part, open source, you have many more possibilities than you have on a proprietary platform like Windows if you want to tinker around with it.