Jim Keller did say essentially that, and I think this is proven in two different facts.

First, x86 hasn't directly executed x86 instructions in a very long time.

Second, Rosetta 2.

ISA doesn't matter. Logic matters. Cache matters. Branch prediction and speculative execution matter. Buffers matter. Instruction reordering matters. Node size and packaging matter. SIMD matters for some workloads. Etc.