I’ve just installed iOS 12 in my iPad mini 2nd gen… quite old I believe it is from 2013. Well… I installed iOS 11 in the fifth beta and was waaaaaaay too slow. Almost unusable. The keyboard was super laggy and switching apps was a pain, to give an idea, it was like the iPhone 4 running iOS 7.
But with this beta (1st public, 2nd for devs) it runs pretty well. But? Obviously, but is pretty usable, and launching the app switcher or going back to home, loading apps seems more responsive even than iOS 11.
Maybe Apple should switch to a two years period between mayor releases, this can give enough time to produce a really polished OS. Let me explain.. iOS 11 is barely reaching its maturity, is quite polished but, surprise, is about to be replaced by a less stable version.
iOS 12 looks promising, but you know that we are (everybody) now running beta software all the time?