The problem here is a severe lack of quality data. The best we have right now is SPEC2006 which is unfortunately only single core. You're absolutely right that it makes more sense to compare like for like in workloads, but we don't have any good multithreaded cross-platform benchmarks. There's geekbench, but it's somewhere between mediocre and shitty. And then nothing else? There's then no multithreaded benchmarks that also have measured power draw on an A12/A13.
A 4800HS at it's 4w/core all core load is also still clocking higher than an A12X. When Apple has the thermal budget to spend as well they'd almost certainly do the same thing?
> A 4800HS at it's 4w/core all core load is also still clocking higher than an A12X.
This doesn't mean that much, since the range of efficient clock speeds depends on design choices, so they aren't always 1:1 comparable between architectures. Apple might well increase clock speed on their desktop chips, but unless it's only a few percent, it won't be as simple as pumping more power into the same dies; they have to actually redesign the core to operate efficiently at those higher speeds.
Hence it makes much more sense to treat the A series processors as 2 watt chips when looking at multi-core scores. They're targeting efficiently hitting these lower frequencies. You'll get a similar result for the 4800HS; it'll use a lot more than 4 W single-core.