As another datapoint Ian (of Anandtech) estimated that the M1 would need to be clocked at 3.25Ghz to match Zen 3, and these systems are showing a 3.2Ghz clock: https://twitter.com/IanCutress/status/1326516048309460992
The 5950X cores are actually reasonably power efficient. Anandtech has nice charts here: https://www.anandtech.com/show/16214/amd-zen-3-ryzen-deep-di...
TL;DR is that 5950X cores draw about 6W each with all cores loaded at around 3.8GHz per core. They scale up to 20W in the edge case where a single core is loaded at a full 5GHz.
> And the M1 is running at a lower clock.
Comparing a power-optimized laptop chip to an all-out, top of the line desktop chip isn't a great way to compare efficiency because power scaling is very nonlinear. The AMD could be made more efficient on a performance-per-watt basis by turning down the clock speed and reducing the operating voltage, but it's a desktop chip so there's no reason to do that.
Look at the power consumption versus frequency scaling in the Anandtech chart for the 5950X: Going from 3.8GHz to 5.0GHz takes the power from about 6W to 20W. That's 230% more power for 30% more clockspeed. Apple is going to run into similar nonlinear power scaling when they move up to workstation class chips.
If you really wanted to compare power efficiency, you'd have to downclock and undervolt the AMD part until it performs similarly to the Apple part. But there's no reason to do that, because no one buying a top of the line 5950X cares about performance per watt, they just want the fastest possible performance.
Comparing to an upcoming Zen3 laptop chip would be a more relevant comparison. The Apple part is still going to win on power efficiency, though.