The ISA can massively impact performance on relevant real-world workloads, but the divide isn't along the mythical RISC vs. CISC divide. Take H.264 encoding as a contrived example and try it with different x86 ISA levels (e.g. no SIMD vs. SSE2 vs. SSE4.2 vs. AVX256 vs. AVX-512 on the same Zen 5 desktop CPU. You can't just build a 32-wide OoO core and have it run at a useful clock speed.