I think few of us really imply that the performance will be horrible NOW, it will be very good at least for a casual user/consumer. But many of us (those unhappy with 2 GB RAM) are afraid that these new devices, that didn't even star to sell yet, will begin "choking" after exactly the same iOS upgrade that will prove "too heavy" for your venerable iPad Air2 once in the future, after having much shorter useful life than your device.
Not to say your device cost somewhat less for the comparable configuration when it was a new model and is even cheaper now, therefore probably still is a better purchase for those who don't need a pencil and a new keyboard, just want an iOS tablet. RAM the same, bluetooth and WiFi the same. I don't really think that the difference in performance between A8X and A9X will be the thing that will seriously affect the average user experience or will make new 9.7's "retire" much later than your Air2 (though of course I may be wrong).
USB2, camera bump on a _tablet_ (don't really care about it on my iPhone6S Plus) and that shameful marketing babbling about Win PC users going to switch to this "Pro" "future of personal computers" are additional cherries on top of the cake of our impressions.