There are already benchmarks showing (sometimes, for certain workloads) mobile phones outperforming x86 laptops.
You can read claims like "Geekbench has the iPhone 7 beating the $6,500 12-core Mac Pro in single-thread" [1] and "new iPad Pros are faster than 92% of all laptops, tablets, and convertible PCs sold in the last year" [2]
Of course, I doubt that generalises to all workloads.
I have a custom todo app written in clojure, and I ran it on one of those "linux on android" apps on my new phone the other day... it ran WAAAY faster on my smartphone than on my laptop, to my shock (admittedly my laptop has a Celeron processor, but still...)
No, it's true. What Apple does is partially pay more square mm of silicon for the same performance to reduce power, and partially things like restrict the use of small page sizes to allow VIPT L1 cache. And partially the ARMv8 64 bit architecture is a ground up redesign intended to used in modern high end architectures, though that's a smaller factor I think.
If you're only needing that compute power in burst mode, it's fine - and a laptop/PC with actual fans and heat sinks can push quite a lot more out of the same chipset.