IIRC the low power states of M series chips generally dips down further than most x86 CPUs do, and the way both the SoC And OS are designed are for racing to idle and coalescing tasks to reduce wakeups. On the MBPs specially the screen can also drop down to 1hz so the GPU isn’t wasting cycles redrawing static content.

The result is that in more typical usage where the machine isn’t under a constant load, battery life is much better. When it’s sitting there idle displaying a web page it’s barely consuming any power at all, where most competing laptops at minimum are pulling at least 2-3x as much power between the CPU not being able to scale down that far and constantly getting woken to perform poorly scheduled tasks.