The 11” pro and the 9.7 6th gen are very similar in size because of the smaller bezels. So that’s where my concerns stem from when comparing the rigidity of the two. I understand the bigger you go, the easier they can be prone to more flex.When I took my old iPad Air 2 out of its case to sell on the top part which was plastic (cellar version) was really warped along to top edge, I had it from launch and it was always in the Apple smart case. My 1TB 12.9 cellular has some flex but nothing major, I tried flexing the Air 2 and that two had some flex too, basically the bigger that iPad the easier it is to flex but its still as straight as when I got it and its used every day. Best iPad I have had and i'm not at all concerned about durability, its in a great STM sleeve (super padded and water resistant) for when I go out case and its also in the Apple folio too. I was concerned about durability, but I'm more than happy with my purchase.
Like I said, for all I know, if and when I get one, it’s perfectly fine. But apples response to the issue wasn’t very reassuring if I was to encounter a problem with bending either. Which is a shame because the main thing that’s held me with Apple over the years if their warranty service