The easiest point of proof is looking at how well the iGPU performs looking the perf/mm2 and perf/watt. The ARM GPUs do significantly better than both AMD/Intel's efforts. And Apple is at the top.
Ahem, IMG Tec is standing behind you looking very angry indeed.....
GPU and CPU are not comparable targets - I mean at all.
By AMD's own admission they would ideally use different optimised process nodes for CPU and GPU components within an APU, but obviously cannot do so in a monolithic design.
It does stand to reason that HW optimised for a mobile first use case would emphasize area and power efficiency - it took them years to catch up to x86 however, and the benefits are as yet not such a massive advantage truth be told.
The 105W of an N1 64C ref design is certainly impressive - but lacking SMT of EPYC 2, and still not dramatically more than 2x the power efficiency per core, to say nothing of the SIMD limitations of N1 vs EPYC 2 also.
Apple/PowerVR is "at the top" because they took a base IMG Tec design and tricked it out exactly as they wanted it, rather than using a synthesizable licensed OTS core that anybody can just drop in to an existing SoC design layout, coupled with having explicit control over the platform it is used on, not entirely dissimilar from game console full system stack optimisation. Fully controlling the stack has its perks.
The ARM community has the benefit of not suffering from the more direct and caustic competition that the main x86 vendors do - you can say that Apple competes with Snapdragon until you are blue in the face, but that doesn't make it any more true, because they are not competing on the same platform, and people who buy Apple are fairly unlikely to buy Android phones in general in my experience.
Huawei Kirin and Samsung Exynos do compete with Snapdragon, and now all 3 SoC brands will employ ARM Ltd CPU cores going forward - so in the end ARM/SoftBank receive all the financial benefit from their custom, just as they receive a benefit from the ISA license to Apple, unlike with Intel and AMD who have to cross license from each other to maintain license equilibrium post x64, so likely neither has any particular advantage from it anymore (I bet Intel curses the name Itanium now).