Diancie isn't going to be using diamond storm very often, and seeing how it has three special attacks compared to its one physical attack, maxing special attack EVs is more likely to be useful than splitting EVs between its attack stats. When Keldeo is replaced with Cloyster, the team's user loses out on the opportunity to check a lot of things that are slower than Keldeo, including Blacephalon, Garchomp, mega Charizard Y, Victini, Volcarona, black Kyurem, Zygarde, therian Landorus, and Excadrill. Celesteela isn't a good acrobatics sweeper no matter what. It's simply too slow. If he/she/it wanted an acrobatics sweeper, then he/she/it would be using a Hawlucha.
