Following the introduction of iOS 7 back in June of 2013, a common complaint from developers and designers was that the system animations took to long to complete, making the interface feel slow.
Apple sped up the animations before release, but for some they still felt too slow. Since iOS 8 didn't fundamentally change the animations curves, that perception has lingered. Recently, to highlight the difference between pre-iOS 7 and post-iOS 7 animations, Omni developer William Van Hecke made a video:
Did a crappy iOS 8 vs. iOS 3 vidja https://t.co/SWmRdURSGq— William Van Hecke (@fet) March 3, 2015
Van Hecke attributes the difference to a change in interruptibility — Springboard previously allowing you to act before an animation finishes versus now making you wait until the animation finishes before you can act.
It's my understanding, however, that iOS animations have never been interruptible. They simply ended quickly pre-iOS 7 and now, post-iOS7, they ease out.
Whether shorting the animation tails or making the animations interruptible is the best way to reverse the feeling and the perception of slowness Hecke refers to, I don't know enough to say. Either way, and to his credit, Van Hecke filed the issue with Apple's bug reporter:
@reneritchie 19318009 (Behaves Correctly) and 19377939 (Duplicate)— William Van Hecke (@fet) March 4, 2015
More information on the animations from former UIKit engineer Andy Matuschak:
@fet (except the Springboard unlock animation—that one really was interruptible before). In short: "it's too hard!" Womp womp.— Andy Matuschak (@andy_matuschak) March 3, 2015