Comment by giantrobot

One of the ways both macOS and iOS get good battery life is burst-y CPU loads to return the CPU to idle as quickly as possible. They also both run background tasks like Spotlight on the e-cores whenever possible. So some process maxing out an e-core is using a lot less power than one maxing out a p-core. Background processes maxing out a core occasionally is not as much of a problem as a lot of people seem to assume.