While I gotta say that iPad Air 2 is impressive (just bought one myself) the Ember benchmark where i7 is only ~20% faster is deceiving.
Let's take Octane 2.0 for example, you've included scores for it in your graph.
My desktop i5 (3570) scores ~33K on Chrome x64 on Windows 8.1.
That's 3.5 times faster than iPad Air 2.
Which, considering the clock speed - almost exactly 3.5x of the iPad Air 2 (it's overclocked) - isn't that impressive, I'll give you that. But it's still way faster than 180ms vs 225ms of the Ember test would indicate.
I guess you're reassuring yourself that going Web was a good decision. Long term, I agree.