Sorry but that's simply not the case that the same results would happen. Plenty of people have done fresh installs aand came away without issues that they might have had before. And some people have certainly had issues while others haven't, at least not the same ones and/or to the same degree. That's been th reality for a long time. To try to imply otherwise is to simply ignore basic reality.
The only thing that can vary is internet speed, everything else is a common denominator. Until you start loading apps / changing settings...what you're saying is simply not the case. Identical hardware, will yield identical software performance, unless there is a defect.
I loaded fresh installs when doing my own testing on iOS 8 vs 9 and didn't change any settings. If you had done the same test with the same phone hardware, your results would be identical to mine.
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