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.