A video that cherrypicks one aspect of one app with dramatic slowdown does not make the entire OS slow. iOS 8 runs almost perfectly on my iPad air. That video is equivalent to lighting a candle and screaming like your whole house is on fire.
I noticed the laggy control center on 7.1, and it's fixed on my iPhone 5 with iOS 8. It's buttery smooth now. FPS fluctuations bug me to no end, which is why I'm happy with iOS 8- almost no stutter on my phone whatsoever. Opening a folder after rebooting causes some stutter, and sometimes loading heavy apps takes a tad bit longer than it did on iOS 7. Other than that, it's great.
If you want FPS problems, try opening apps on the iPhone 4 with iOS 4.3. If you opened an app that was located on a screen with all the rows filled, the animation would give you about five total frames if you were lucky. Thankfully it was fixed in iOS 5.
Iphone 5 (and up) is fine in terms of smoothness and performance. It's the iPads. There are some pretty big issues with performance and smoothness on iPad Air and mini retina.
Also, screen rotation stutters when keyboard is on screen on iPad air. The same happens when rotating screen in the App Store app. Opening cc when keyboard is on screen is embarrassingly laggy.
This not nitpicking...