The efficiency doesnt come from the os but from the soc. A steam deck running windows performs the same as a steamos one. And an ally running chimeraos (like steamos) will perform the same as a windows one. Source: I tried it. The only thing thats really hindering low watt performance is the gpu of the ally not downclocking below 800mhz. There is no way the ally should use almost 3w for the gpu in games were the deck uses like 0.5w for the gpu and 3-4w total. But it seems nobody cares enough to fix it.

Other than that I wouldnt recommend the ally. Stick grind is real and after a couple hours the sticks will feel worse than the ones of cheap 1$ ps2 knockoff controllers. Also getting annoyed by constant updates, feels like every week either armoury crate, bios, myasus or windows wants to do some update that takes like 20 min. Which is horrible when you want to use it once a week for an hour or two. And yes you can ignore some. But for example latest armoury crate update simply wouldnt display any of my games until i installed it. Yes I could have started them directly through steam, but that kind of just postpones the issue.

Really the only good reason for the ally is plugged in 30w performance and vrr on the display.