The off the shelf user experience is so much worse though, it doesn't feel like a finished user ready product if you're having to navigate windows UI on a tiny screen with a thumbstick mouse.

Not to mention that running windows ruins the ability to play low power games at low power draws. A game like Stardew on the steam deck draws 5-7w, while the ROG Ally pulls about 15-17w to run it with the same settings. Disabling everything you can through task manager can reduce that power usage difference by maybe half, but there's still a lot of unnecessary power draw just from it running windows.