The real question mark is over the Supply Chain
I have seen at least one article on this matter that has touched on the real point of concern. Given that:
1) People have reported and demonstrated that the iPhone 6 can be easily bent
2) Apple's claims that their testing of their design establishes that this is impossible
and 3) 3rd party testing supports Apple's claim
All 3 of these facts cannot be simultaneously true. Ergo unless you can establish definitely that one of these facts is actually false, there must be some other factor in play. One such factor could be in the Supply Chain.
Apple may well have ensured that their design is robust. The 3rd party testing may confirm that this design is robust. But if Apple have a less than iron grip on their supply chain, then it is highly plausible that there are some iPhones in the hands of the public which do not actually conform to that rigorous design and these are the bendable ones.
In effect, some people buying an Apple iPhone 6/6+ are actually getting a Chinese knock-off (albeit with the same innards). Effectively, sub-standard iPhone clones, but with the regulation eye-wateringly gouged retail price.