I think the home button delay when closing an app on the iPhone 7 might be intentional rather than a bug. That delay is normal on every iPhone before the iPhone 7. Only the iPhone 7 was that fast on iOS 10.3.3 when closing apps because of the capacitive home button it no longer had to wait for the second press (in case you wanted to go to the task switcher, not sure how it worked though.) Because of that, there was an odd jump when you would double press and enter the task switcher. It was caused by pressing the button once -the closing animation begins- then pressing it again - the animation changes directions from closing the app to the app switcher. This caused a weird glitch which some would say is worse than the delay. So, I think it may have been a somewhat hard decision made by Apple, that they would rather have the task switcher perfectly smooth and a delay in the home button.
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Personally though, I was okay with the glitch when entering the task switcher while inside an app on iOS 10.3.3. Because I knew that it was caused by the phone switching in the middle of an animation, it made the phone feel EXTRA fast! That was Apple’s intention when they allowed an animation to be interrupted mid-animation and changed.