Really? AMD's recent moves with Zen/Zen2/Zen3/EPYC look like a big step forward. Zen2 chiplets are the biggest change in years. Zen3 IPC is supposed to be significantly better than Zen2 (17%). The previous gen Ryzen was like 15w TDP, where as the A12Z in the Mac Mini ARM is 15w TDP, but the Zen crushes the A12Z Bionic on benchmarks.
It's difficult for people to remember, but ARM came from really terrible performance to a spot where it is getting in the ballpark of x86, so the advancements look impressive, but that's like saying if I go from $100 to $200, the gains look impressive, whereas you only went from $10000 to $11000, it looks like you are standing relatively still in comparison.
But x86 architectures are decades of maturity, so someone getting a 17% IPC lift (Zen2->Zen3) or a massive reduction in TDP on such a complex chip, isn't stagnation, it's actually MORE impressive IMHO.
ARM is going to reach marginal returns, and soon the yearly perf boosts won't look as impressive anymore.
In the end, I think we'll see convergence of performance. ARM will still have a power advantage on mobile, because they don't have so much backwards compatibility legacy that x86 has to support. However, are Macbooks and Mac Desktops going to be performance and price competitive with Linux x86? I doubt it.
First of all, ARM vendors haven't even come close to the GPU performance of NVidia or AMD's discrete GPUs. An ARM A13 or Mali is not going to compete with a laptop with an RTX 2060, 3060, or RDNA1/2. And secondly, just looking at AMD, it's possible to lift performance / watt still in x86.
I think the laptop space in the x86 realm is still exciting, because of what AMD and NVidia are doing.