I fully remember all the weather app complaints as well as all the 6+ complaints for the entire life of iOS 8. Nearly all of the lag advocates seem have forgotten or ignore it because it's old news and hold 8.4.1 as the pinnacle of excellence. Which is why I said "on par or better" since it has somehow been the bar to reach.
Who cares about the weather app in iOS8 compared to the ENTIRE iOS9 OS stuttering/input-blocking? Put it in perspective, honestly I don't remember or cared about the weather app in iOS8, one can easily replace it with a 3rd party app if needed.
Most importantly, the big emphasis put on 8.4.1 at least on the OP topic is the input-blocking, the fact remains that iOS9 added input-blocking on a very important part of iOS resulting in less fluid usage and that still remains unfixed.
And by the way, pinnacle of responsiveness/performance is probably iOS 3-6, I remember my iPad 4 was a speed demon on iOS6, and iOS7 ruined it, simple things like the keyboard felt sluggish.