I don't see your comparison as relevant. I'm a metre away from a nine-year-old Android 6 phone that can easily go a month on a single charge (while tracking its location!). Your Apple Watch is (a) constantly using its radio, (b) running a fairly high-end graphics chip, and (c) actively probing your body at intervals. Nothing to do with software.
I think you lost the actual comparison. Is not about Android and iOS.
Is about having a ton of mini specific "computers" vs. the very generic conscience.
For example all the balancing, background hearing, hungry, thirsty , and so on are very specific zones in the brain. While our conscient mind is doing...well, whatever we like in a very generic way, basically keeping the joy of living on.
