How is it doing fine? Apple is doing laps over Intel because -- it seems -- of their choice to use ARM. Would they have been able to design an x86/amd64 CPU just as good?
AMD processors are essentially equivalent to M1 in performance while still keeping x86, so probably yes (there are an ARM advantage in instruction decoding, but judging by performance differences, it's probably small).
Apple's advantage is mostly that Apple (via TSMC) can use a smaller processor node than Intel and optimize the entire Mac software stack for their processors.
And vice versa.
Perf/Watt?
DRAM, storage, networking, gpus, accelerators, etc are all eating huge chunks of power. CPU's tiny in comparison. Maybe you save 5% across a datacenter using those fancy unicorn wafers.
AMD's listed "15W TDP" is irrelevant to the observed wattage and frequency (or performance) curves.
And we've seen Apple's A12, A13 on a similar TSMC 7NM node - older if I may add so AMD garners what little improvements are made on that process since then.
Here's a fairly telling chart on the performance: watt curves. https://hexus.net/media/uploaded/2020/8/f5957fa8-630f-44be-b...
BTW: it doesn't improve too much on Zen 3. Slope is just not ARM, much less Apple-tier.
Inevitably someone will chime in and point out AMD's power efficiency is subpar due to boosting far beyond optimal points on the curve; while true this is inefficient we can truncate their frequency to Apple's 3.2GHZ or merely observe the slope of the p:w curves above - at almost any point on the y axis, an A12 or A13 will be taking AMD to the woodshed on performance per watt. And I'm not exactly amicable to handicapping the comparisons by giving AMD & X86 a half decade to work out the architecture before things are "fair". As it stands, Apple's architecture is simply more performant.