What impossible criteria have I placed? I simply said a photo shot on 5s, 6 and 6s would have to be done in the same location and light as the 7, 7+ in order to be properly compared. You are trying to say a comparison from a googled photo taken years ago, in a different location and in different light is a proper comparison and claiming they would have taken exactly the same quality photo as what the 7 took based off something done in totally different conditions. You are seriously dense and have no grasp on logic in general.
It is NOT impossible to have a iPhone 6 in hand and an iPhone 7 in hand and take two photos of the same scene in the same light, milliseconds apart. THAT is what a fair comparison would be and would determine if your claim of the older phones could take exactly the same quality photo. What ISN'T a fair comparison is your claim that because you googled a photo taken years ago vs one today look similar, therefore means they have identical quality in taking photos is complete and utter BS and you have no idea at all what you're talking about.
By your logic there are now absolutes for camera settings in any given situation. Please use google and tell me the exact shutter speed, aperture and ISO that were used in the sample photos since there are no variables (according to your own logic) and please point me to this magical book that lists all these set in stone setting values for photos with sun, or cloudy or whatever. Spoiler, there isn't because there are far too many variables.
Anyone with a shred of common sense could look at photos shot with older iPhones (and other smartphones) shot in similar situations with similar settings can do a comparison. You, on the other hand, are so terribly desperate to win an argument that you place impossible demands. It doesn't take much work or intelligence to do "yeah, but" scenarios.
Plenty of people on here have the common sense to look at the vast number of past photos to compare for themselves. Obviously you don't have that ability so let's leave it at that.