M1 machines do have better battery life (i think the m1 chip itself is 10W?) And a bigger battery by virtue of being in an ipad or a full laptop, as opposed to being crammed in a handheld. There's also the advantage of being an arm64 machine over a bloated x86_64, notorious for the complexity and power draw
But also you have to consider that m1 macs don't offer you 8 zen3 cores and 8 rdna 2 gpu units. Apple device are notorious for being less powerful than the competition, but making it up in software, which you can't really do when the task is gaming, since that is basicaly as close as a full synthetic benchmark you can get.
Disregarding the arm/x86 compat layer that would be needed to play most games and its overhead, getting anywhere as close to steam deck framerate would probably take about 25 W worth of m1 chips. For 20 W, this thing is actually a beast. Like seriously, it runs Elden Ring (almost) well.