The pictures you took that are in that thread don't really give a good example of what you are describing outside of maybe the first one (where the 6 Plus clearly shows more detail in the surface of whatever that is you took a picture of).
Bottom line, as a person who is a stickler for the cameras on these devices...the 6 Plus camera is fantastic, and to me, is the best camera that has been put on an iPhone to date. Here is a good example of the differences in ability...last season I had my 5S AND my 6 Plus at a Braves game, and I took a picture to show the difference in camera ability for my own curiosity.
iPhone 5S
6 Plus
...all that said, if you're concerned about your camera performance, make an appointment with the Apple store and have it exchanged...this camera on the 6 Plus is fantastic.