To be fair, it is the number one complaint that comes up on forums. "Fragmentation" used to be popular arsenal too, though that has died down some.
----------
When I swap into landscape mode, spotlight lags (or it's rought or choppy or whatever you prefer). There are videos of this too. I have tried it on a few store displays.
Playing a movie in Safari and swapping to landscape also causes a stutter. I can reproduce this on store displays too. Every time. Playing the same video in another browser (specifically Mercury) does not do this. Obviously this isn't something I can test on a store display, and I am the only person I personally know with a plus. I think that is decent evidence that, at the very least, that one quirk is software related, not hardware.
I don't believe my phone is faulty. I am basing this on my own personal experiences with quite a few devices now (store displays). I am not saying your experiences are wrong or you are lying, but I am saying that my personal experiences are just that, my personal experiences. They are enough for me to whole heartedly believe that the issues I have seen are not related to a fualty device.
You do make a great point, though I don;t know why you made it. Yes, it is reasonable to expect with a new OS that there may be quirks. I am expecting that and it is a valid reason for not expecting Apple to just hand me a new device, I would think.
So try it again right now. Open a youtube video in Safari look at it horizontal, then switch to landscape...
Does it happen every time? I JUST tried it, and was gonna say its forgivable if its not the smoothest because even a mac pro has a pause when it messes with changing resolution or screens...
but i swear it just rotated with the most beautiful and smoothest motion.
Now the spotlight thing i was able to reproduce.
But spotlight is loading something heavy. Its done that since it first was on iPhone, I don't think they can ever fix it or make it smooth lol.
But stuff like that hardly makes it "a thing" to the tune of how people act like the phone isn't the smoothest phone ever in general day to day use.
Its also gonna get patched more and more until eventually its as smooth, stable and bug free as the 5S became. Its just a normal/reasonable software cycle.