ISA does matter in a CPU design and CPU performance:
- Variable instruction sizes make the front-end more complex and limits the decoding width;
- Delayslot makes superscalar front-end more complex;
- Page size limits VIPT L1 cache size;
- Dedicated SIMD/FP architectural registers allow dedicated SIMD/FP physical register files;
...
The choice and design of the ISA is extremely important,
it's hard to argue that the ARM ISA has no impact on M1&M2 performance.
But the ISA choice is obviously not enough to explain the whole performance of the M1&M2.
Likewise, the manufacturing process cannot fully explain the performance of the M1&M2.
The Apple microarchitecture is by far the most performant and efficient of all high-end superscalar CPU.
But be careful with simplistic explanations, the microarchitecture is always constrained by the ISA/architecture, and the x86 ISA has some flaws that can affect the microarchitecture (least on the power consumption).
