Judging by this and the tons of other videos, I'd say this is fairly easy to bend. Will consumers intentionally bend their iPhone 6 + in this manner? Of course not. But within time and normal use, like storing it in the front pocket, where 99.9% of people store theirs, sitting down while in the pocket, and taking it in and out of pockets, I guaranty that the 6 Plus will eventually bend, or at the very least deform some. It's the nature of aluminum which weakens in time, and obviously, Apple didn't do enough to reinforce it. It is structurally unsound near the volume buttons.
Return the 6 Plus for a regular 6 while you can. You'll thank me later.
How easy was this:
https://www.youtube.com/watch?v=h-DcUASffHU