AMD servers are already below 3 watts per core. ARM doesn't actually confer any power advantage. Most ARM processors use less power because they're slower. Apple has a slight advantage because they use TSMC's latest process nodes, but it isn't very large and it isn't because of the ISA.

I was looking at EPYC chips from 2-3 years ago and those do consume more like 8-10W per core but you're right. The latest EPYC 9005 are actually quite efficient.

EPYC 7702(P) is only slightly more than 3W/core (it's 3.125) and that's from 2019.

But the newer ones use even less and they're faster.