Intel is learning (or knows, depending on your perspective, see goldmont) how to build highly efficient cores too, but like ARM haven't quite figured out how to build a super high performance one that is crazy efficient. ARM's continue to be quite efficient but not particularly performant, while intel's continue to be quite peformant but not particularly efficient.

Either way, the trend is pretty clear at this point more power dissipation=more performance.

Code density is important, but you can just double the icache. Given that icache is often smaller than dcache, it seems that's not the major bottleneck.

Also, if code density is so important, why did arm drop Thumb when they switched to 64bit?