Respectfully, as a person who once agreed with you, I would say that you can't possibly really know this until you actually USE a 6/6S for a couple weeks, all the time. You might be shocked at how quickly your hand adapts and finds the new size to be just as natural as the old 5S size. I was shocked.

This is a very good point, but I have a counterpoint: I suffered through a year with the 6 before downgrading to the 5S last month. My only regret? Waiting so long to ditch the 6.

Human hands don't need to spend a week to learn how to correctly grasp an object, at least not one the shape of a phone.