That's the thing, iOS 8 (and really the latest versions of it that were out close to a year after the fairly bad initial versions of iOS 8 were out), still lacks in performance compared to the latest version of iOS 7, and that lacks in that area compared to the latest version of iOS 6--might as well compare things against that and basically still be unhappy that ever since the first version of iOS 7 has been released, even years later, things are still not as good as far as performance goes when compared to iOS 6.
Plenty of those statements from plenty of iOS 9 stutter/lag threads. That's not say everyone has been saying that, just as not everyone has been saying that things are "flawless".
You might not recall that, but plenty of people do (and way more complained about all kinds of issues than there have been complaining about stutter/lag on iOS 9).
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In any case, not really what this thread is about, so no point of going down deeper this all too well and repeatedly traveled path.