the A9 was used because its a general purpose processor that can do everything unlike M3's that are just use for radios etc.
Why nit picking about its architecture - as long as it delivers what it says who cares how it does it.
the new Exynos will be the better chip I agree - but it won't be in the transformer 2 so thats where it will lose out for me.
No one has copied the transformer concept - and until they do they can stick their super duper SoCs.
I probably nit pick because I'm a geek, and through work reasonably heavily exposed to arm soc's,
The A7 makes more sense than the A9 though, it is as you mention a full featured core, yet lower power...
I just think, as a geek again, that the use of an A9 5th core smells of bodging <something> to get decent power consumption.
Ah, and now you change the ballpark and introduce the transformer concept, and yes you're right that's unique and overrides the SoC used...