I just came across this thread. And it’s so sad. I tried scrolling through the app switcher as fast as I could on my iPhone Xʀ on iOS 12, and it has no lag, regardless of how many apps I have in there.
I also tried closing apps by swiping. Regardless of what I opened, it’s so absolutely, buttery smooth.
My iPhone 6s on iOS 10 is blazing fast too! Yeah, Safari is tough to use, many websites don’t even open, but the rest is perfect. Keyboard has never lagged. My 9.7-inch iPad Pro on iOS 12 has occasional and noticeable keyboard lag. It had never done that on iOS 9...