Lighter for what? Displaying a clock?

Add a bunch of fat, semi-desktop binaries that actually provide some kind of functionality to make it remotely comparable, and then you just have a worse, fatter system that runs hot and wastes the battery.

Android is a unified system working together to make the device race to sleep as fast as possible, with as few wakeups as feasible (e.g. batch together events that would wake up the device).

Lighter as SXMO will run on a low budget 1GB of RAM armv7 handheld released in 2014 (maybe even 512MB of RAM), even without 3D acceleration and Android 17 just won't, no matter how much you tweak it