I just read through the entire thread and yep, there is a lag when closing apps. It's only on the iPhone 7 and 7 plus. NOT on any other phone.
I repeat. It's ONLY on the 7 and 7 Plus.
Anyone who can't notice it (on a 7), simply aren't paying enough attention, or are really stupid. Period.
What happened is, on iOS 10, the iPhone 7 would close apps at the exact moment you press the home button. Never did that on previous iPhones. There was always a half a second delay when closing apps. Maybe the 7 was sped up intentionally to make us ditch our 6s' and upgrade. But now with iOS 11, it's back to being a 6s. Meaning it takes half a second to register the "click" and then close the app. That is the problem here. That extra 0.2 of a second.
Shown throughout this video. And this is iOS 11 GM. Not gonna get any better than this.
I've also noticed that with older iPhones, closing apps is actually a little faster on iOS 11. Not always, but sometimes.
Shown here with an iPhone 5s
So there you have it. PROOF that it purposely slows down the 7 and 7 Plus when closing apps.