That's because it's your iPad. Seriously. You can believe what you like but I will believe what I see on the screen in front of me, which is a perfectly smooth animation with no issues whatsoever.
I'm glad it's acceptable to you. You too can believe what YOU like because what I see in the screen in front of me proves my case, side by side.
I had my iPad replaced because the performance drove me up the wall. I cited slow WiFi issues (which I also had) and got a replacement on iOS 7.
The arrogance is you sitting there trying to tell me I'm making something up. I FEEL the difference, I SENSE the fluidity difference during use. iOS 8 slows the iPad Air down just enough in UI terms to make it discernible next to the iPad Air 2.
What you see is acceptable to you. Congratulations. It wasn't to me, iOS 8 made my Air a nightmare to use. And the ones in the Apple Store I tested out before pushing for the replacement proved it wasn't an issue with my unit.
I know if I foolishly took your oh so superior words for granted and updated again, I'd throw this thing off a brick wall within minutes. There IS a difference. iOS 7 IS smoother than iOS 8. Even if it's just a little it's enough. More than enough to matter in terms of user enjoyment.