Maybe? There exist some extreme-performance ARM CPUs like A64FX from Fujitsu.

They are the top performing ARM computers you can go to a store and buy. I'd love to have an HPE Ampere or a POWER tower under my desk, but it's not easy to get anything like those, and certainly not for a price competitive with generic x86.

Are we confusing things?

They're both RISC, but P9/P10/etc is based on IBM's own Power microarchitecture (possibly open sourced / open standard), I wasn't aware it had anything to do with Arm? I could be hopelessly wrong...

Or do you mean something different with "POWER"?

Owning an IBM Power system is a daydream of many nerds apparently.

And power is open in that the ISA is open. Power10 is a bang up to date CPU so the internals are all closed.

There are other interesting ISAs that are not arm64. Sadly, the only ones that still could be viable desktop (more like deskside) are either server-grade ARM or IBM's POWER (and none of them makes Mac Minis).

I would be shocked if an A64FX core could go toe to toe with a Firestorm on general code. It just doesn't make sense for Fujitsu's use case to spend nearly as many gates on general improvements versus more vector ALUS.

The A64FX is a very specific microarchitecture that's aimed at big core counts rather than being a single threaded monster.