I do not think that I have seen any public benchmark for more than a decade that can compare ARM-based CPUs with IBM POWER CPUs.

The recent generations of IBM POWER CPUs have not been designed for good single-thread performance but only for excellent multi-threaded performance.

So I believe that an ARM CPU from a flagship smartphone should be much faster in single thread that any existing IBM POWER CPU.

On the other hand, I do not know if there exists any ARM-based server CPU that can match the multi-threaded performance of the latest IBM POWER CPUs.

At least for some workloads the performance of the ARM-based CPUs must be much lower, as the IBM CPUs have huge cache memories and very fast memory and I/O interfaces.

The ARM-based server CPUs should win in performance per watt (due to using recent TSMC processes vs. older Samsung processes) and in performance per dollar, but not in absolute performance.

After Power9, IBM became uncompetitive multi-core performance against mainstream server CPUs - both x86 and Arm. They didn't keep up with the rise in core counts.

And the single thread side isn't that good either, but SMT8 is a quite nice software licensing trick