Your assumption of perf/w being all that matters is hilarious and ignorant. If perf/w was all that matters, phones wouldn't being using customer cores, A9/12/15/et al. They would be using the lower end ARM chips which are much more efficient at perf/w.
And there are plenty of benchmarks that do support it. Even bad one. None of the mobile products are on the same performance levels as the laptop/desktop products currently in the market. And they aren't really even that close.
No, geekbench is hated because its about as useful as Dhrystone. Its a collection of largely uninteresting kernals that have little to no impact on actual application performance and its omnibus number is completely useless as it doesn't tell you anything because its trying to combine too many disparate aspects including roughly half its value being pointless embarrassingly parallel runs. Its working sets are far too small, even by mobile standards, to be useful. It doesn't model at all any real application load. Nor does it have any actual research behind the including of its parts or tuning of those parts. And finally, the whole thing is incredibly opaque.
If you want to do actual comparisons, run Spec with various compilers or use real application based benchmarks.
A8X/A8/A7 all run exceptionally well in real-world benchmarks. I'm sure you've used an iPhone 5s or 6, or iPad air 2 and noticed how quickly they run. They also beat intel in perf/W in javascript benchmarks. There are literally NO cross platform benchmarks that intel wins when comparing A8X at 3.5-4W and Haswell at 15W in perf/W. Please show me where I am wrong here.
You are correct that Apple has not, and probably can't for the moment match intel in peak performance. That's not what this topic is about, we are talking about a Macbook Air 12" Retina. The discussion is whether or not a A9 ARM Apple designed processor could serve to give adequate performance. In what way is the iPad Air 2's performance not adequate for that kind of device? This would obviously have a higher clocked, higher TDP processor than an iPad.
Apple probably won't ditch intel completely, not all at once anyways. Intel still offers performance that peaks at 5-10x that of peak A8X in their multi-processor Xeon systems. However, that's at 20-50x the peak power draw. So they are not suitable for mobile stuff.
There is no reason for apple to continue using intel in a 7MM 12" form factor. It is, in fact, a poor engineering choice to put a 15W Broadwell or even "4.5W" Broadwell (as evidenced by insane throttling in Yoga 3 pro, a 12" 8mm tablet, even at 3.5W) in this new macbook Air.
There is just no way to engineer your way around that loss in battery volume (over 50%, remember the macbook air was 13" this is 12" and this is also half the thickness) and TDP capacity. Look at what Lenovo did. They are not retards.
IF apple do manage to fit broadwell-U into that form factor with good performance, I will be amazed. That would be an epic engineering feat.