it really depends on what specs you are focusing on. in single thread performance, A8 is already on par with the Exynos 7420. in multithread it is leagues behind. in gpu it is also about on par, but in storage it is again far, far behind. my guess is that apple will again be ahead substantially in single thread, but probably at best match the multithread and storage performance of the 7420. there are also apple-specific hardware features like touchid and force touch that count in a similar way as the curved screen.
i think you are spot on with the iphone 6 being just a form factor change to the 5s, but they really needed a form factor change bad. personally, i am never one to discount apple hardware. the only iphone release that i wasnt impressed with was the iphone 5 and i would hope that apple will come up with something impressive again. that isnt to say that i will ever buy an iphone, because i dont appreciate having my phone locked down and opressed by iOS