I think iPhone 6 Plus is the worst product Apple made. Underpowered and underspecced just like iPad 3. To top it off, the built quality was also questionable with several phones bending on applying slight pressure.
It will never have buttery smooth iOS experience.
With Air 2, I agree that it is an extremely powerful device. Slightly overpowered for this generation some might say. But it just falls short of greatness due to chassis vibration and sacrificed battery life.
My iPhone 6 Plus is fast and smooth with excellent build quality.
Never seen a bended iPhone 6 Plus with my eyes (except people on YouTube voluntarily bending their device).