The thing is all these phones are also coming with 2 or 3 different classes of CPUs in order to save power, those slower cores must be achieving much better Watts per Op otherwise they wouldn't bother and be using all that die space for the faster cores. Clearly they are not doing race to idle in most mobile phones either at this point given they have been using a big/little strategy for over a decade.

What has happened is they realised waking up CPUs to do individual tasks was inefficient and stopped CPUs sleeping so they batched work together but that is basically the overhead of going in and out of sleeping which presumably does waste a bunch of power. This also explains why so many high end phones now have 1 ultra slow core that deals with the background stuff when the phone screen is off, the rest can all just sleep and this low power core can sit there on low clocks sipping minimal power most of the time.