What makes you think that handhelds and smart devices will not hit the same bottleneck soon? Or does Moore’s law apply only to PC processors and they skip mobile processors due to a freak error in Quantum Physics? Just a matter of time, before the SnapDragons and Kirins and Exynoses begin to suffer from the exact same problem (In fact, they already do - the pursuit is on for more cores, less GHz per core, heating problems, BIG.Little and so on).
The iPhone 6S is 10 times more powerful because it started with such a low standard to begin with. A similar argument could be had for Intel CPUs with a 6 generation gap - Compare the current gen SkyLake’s with a Core 2 Quad (6600) etc. - lightyears ahead, without exaggerating, and evidently so when it comes to compute intensive tasks like media encoding or encryption.
Similarly, to debunk the argument that PC processor speeds aren’t doubling every gen - Well, how much is the improvement when going from, say, SnapDragon 801, to 805, then from 805 to the 808, onto the 810. Do you see a doubling with every gen there? Thought not. More like a minuscule improvement, as the synthetics (GeekBench, AnTuTu) depict.
One example for the PC platform, NOT 6 gens apart:
Almost a 170% increase.