It will be butter smooth on iPhone 8 an 8+.Let's see how it performs on the new iPhones. I'll say this, the iOS 10 animations do look much smoother in this case. iOS 11 still feels jerky when you close an app quickly.
Btw you are right. iOS 10 animations were so smooth that they were taken for granted. As someone pointed out, Apple needs to re-write the animation framework or whatever that controls UI animations. One year they fix one animation, next year they break it and fix another one.