The worst part is... over the course of a year, people will adjust to the slowness and their eyes will get used to the stutters and they'll eventually forget how well their iPhone ran before. Even with the small performance improvements over the course of iOS 11, it still will never hit iOS 10 speeds or fluidity, but it might be enough to make people think it's fast again, but all they know is that it's faster than iOS 11.x.
If you're lucky enough to find an iPhone 6 running iOS 8 or an iPhone 5s running iOS 6, you'll see what I mean. Those were the OSes that those devices were DESIGNED to run, just like the iPhone 8 and X were designed to run iOS 11. You'll see that those devices run great on the new OS because Apple only cares about their latest device.
If you're not running Apple's latest hardware, they don't care about you.