I've been trying for the last ten minutes to reproduce any of the problems you describe, and I'm not having any luck. I'm pretty sensitive to graphical glitches, especially on iPhones (for some reason I feel more willing to cut my Android phones slack in that regard, for whatever reason I hold Apple to a higher standard -- probably because $$$). My iPhone 7+ 128GB is just fine, rotates, home button, etc -- all the animations are very smooth.
I think some people just got glitchy handsets. There are too many people who have problems to dismiss it out of hand, but a lot of us got phones that work just fine. Out of all the phones I've bought, only my iPhone 6 had any problems and then it was just a cosmetic defect in the oleophobic screen coating.
I've also owned a lot of Android phones (flagships all of them, though you could argue the Nexus phones aren't necessarily flagship quality) and I think iOS is considerably more polished and smooth than any of them. Haven't tried a Pixel yet, though, maybe that brings the polish on Android up to iOS levels *shrug*.