There are some wrinkles to this: First, big cores are less efficient per unit work because there's a lot of complexity in things like reordering, speculation, a

There are some wrinkles to this: First, big cores are less efficient per unit work because there's a lot of complexity in things like reordering, speculation, and pipelining and that complexity costs energy. A design optimized for peak throughput per time looks different than a design optimized for peak throughput per energy. Second, reducing area and energy for the cores allows spending those resources somewhere else like larger caches which, to a point, can reduce energy further. Third, realtime workloads can't really be delayed without compromising user experience so you're going to be waking some cores up constantly anyway. Might as well have a few efficiency-optimized cores and pile as much on them as possible to keep latency and energy consumption low.