Well yes, x86 macs in those classes were using underpowered Intel CPUs :-). That said, I've yet to see any serious benchmarks of this kind of workload. We know the M1 is fast for single threaded UI code (fast as heck atomics sure help with ObjC reference counting), but that says nothing about SIMD and floating-point heavy audio processing. Rosetta adds overhead to that, potentially a lot vs native ARM code, depending on the code. There is no way to make a blanket "the M1 is so fast it overtakes Intel even under emulation" claim.

I'd personally be more concerned about stability and drop-out issues. Apple sells Rosetta as an "ahead-of-time" translator, but that is necessarily best effort (because true transpiling is not a solvable problem, e.g. self-modifying code). Thus, there is always the possibility that the JIT gets invoked in the middle of the audio processing thread, and that won't end well for real-time guarantees. There are also programs that just don't work under Rosetta properly (for unclear reasons).