The designers of the "settings" screens in Windows should be utterly embarrassed. They are pathetically useless, especially when compared to their predecessors apps like the MMC.
The responsible monstrosity is none other than UWP, which also added a loading screen to the Calculator.
I believe that animations are partially responsible for the slowdown, and Windows is not the only offender here, iOS and Android are just as much guilty of this. In most cases, animations when opening apps, switching screens, etc. don't add anything to the UX.
The new one actually does the same for once, but I often use it to jump to the menues of the left. At least those weren't replaced yet. The new ones are just dreadful.