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.

The level of talent Apple has cannot be understated, they have some true CPU design wizards. This level of efficiency cannot be achieved without making every aspect of the CPU as fast as possible; their implementation of the ARM ISA is incredible. Lots of companies make ARM chips, but none of them are Apple level performance.

As a gross simplification, where the energy/performance tradeoff actually happens is after the design is basically baked. You crank up the voltage and clock speed to get more perf at the cost of efficiency.