Yeah, battery life varies greatly. More demanding games are in that ballpark. Sometimes you can squeeze more out by reducing the graphics settings and ensuring you have a set framerate cap. Older and less demanding titles get a lot better battery life. It can get 6 hours in something less demanding IME.

You can also easily use a physical keyboard and mouse with the Steam Deck either through Bluetooth or any old USB C hub. Video out works too and it supports MST so it's possible to do multiple external monitors even though it has a single USB C port (can't be done with M1!). It has a full fledged desktop mode that's basically just a normal distro with KDE. By default you can't use pacman to install Arch packages but you can easily enable it if you want. Flatpaks are easily installable by default though.

I'm not sure M1 would be much more efficient playing AAA games either. Some of the battery life advantage is just the fact that they have more room for more battery.