The reason I mentioned the individual pixel size was because Apple, in the past three to four years have mentioned not reducing the pixel size to 'pack in' more pixels. Larger pixels gather more photons, they said. So, we have now reached a point where, due to space constraints, the pixel size has decreased from 1.5 microns (6 & 6+) to 1.22 microns (6S & 6S+). So, I'm guessing they have reached a point with the software picture processing to achieve the same or better performance with the smaller pixels.
I guess we will soon see the results with some third party testing of the cameras.