Occasionally I flash a pixel device back to an old firmware.

Every time, I am surprised how speedy and lag-free it feels.

I would really like a 'security updates only, no other updates' phone, because I value speed over some UI redesign or whatever is in the next android update.

I realize my experiences are anecdotal to the two Pixel 4a phones in my family, but the numerous reddit threads about the Adaptive Battery issue (4a) and the later unexplained stand-by battery drain (4a & 7) seem to show that I have at least not been the only one experiencing this.

Android has been having battery drain issues since forever. All it takes is some random app, library, system service or driver to get into an infinite loop waiting for something that will never happen, and suddenly battery life is cut down from multiple days to just a few hours.