The only way to escape the Apple lag completely is to buy a new device every year. It will never run as fast as how it used to on the original OS it shipped with. With all this marketing hoopla about the A11 Bionic, only to be crapped on next year by iOS 12 with delays and stutters making it look like a midrange Android phone. My second gen 2017 iPad Pro 12.9 will stay on iOS 10 because I don't care about the productivity features to lose he smoothness of the device by upgrading to iOS 11. 4 times Apple has tried to trick me into upgrading by downloading iOS 11 in the background without my permission and popping up the update box which is so easy to press okay and enter into LagOS 11 but I shall persevere. You are not ruining my iPad Apple and I will fight your update prompts if it's the last thing I do.
my SE absolutely runs better the past year (ios 10 AND 11) than it did when i first got it...