> In most cases, efficiency and performance are pretty synonymous for CPUs. The faster you can get work done (and turn off the silicon, which is admittedly a higher design priority for mobile CPUs) the more efficient you are.

Somewhat yes, hurry up and wait can be more efficient than running slow the whole time. But at the top end of Intel/AMD performance, you pay a lot of watts to get a little performance. Apple doesn't offer that on their processors, and when they were using Intel processors, they didn't provide thermal support to run in that mode for very long either.

The M series bakes in a lower clockspeed cap than contemperary intel/amd chips; you can't run in the clock regime where you spend a lot of watts and get a little bit more performance.