I think we need to define "lag". I think we need to define "stutter". These words are being tossed around too loosely. For instance, my iPhone X lags a bunch. Tap the screen, swipe up to access my home screen, swipe through the home screens and its "lag" or "stutter" central. It doesn't happen every single time, but it happens a few times a day. It seems as though Apple has been apart of this "lag" and "stutter" fest for a few years now.
They had the crown ios 6 and below for being very fluent and stable. Once they started adding "features", that's when the hiccups started to show its ugly head. Definite crashes upon launching apps. OS would start to freeze here and there. When I had the Note 8 for a month, I didn't experience any of the so called "lag" issues. However, people say it starts lagging after a few months in which I cant comment on since I never had an android for that amount of time.
Apple's lag issues seem to skate by because of the reputation they've built for being a very fluent, solid OS. However, that has not been the case in awhile. Mean while, android came into the game laggy as all hell. However, they've been putting in work and getting better year after year. Hopefully, apple can iron out some of these issues in iOS 12 but you know....we say the same crap every year because of that "reputation".