There’s many that would claim iOS is terrible and has been for a few generations, I’m not 100% one of them but I don’t think it’s as good as it can be, moreso when the X comes out.
As for a comparison, I’ve been on ios11 on my 6s for about 4 months now and it’s not slow enough for me to consider changing (I would if there was something better on offer but the 8 and the X just don’t cut it) unless I compare an 8 directly next to my 6s I’m not going to feel “how slow it is” because in reality it’s not and I think a lot of people are thinking that these days.
Apple are most certainly pushing the price, it’s what happens when you go to a rival for a screen. They’re not going to take the hit on what Samsung are charging, that gets passed on to you and me.