You would be correct in saying this, however, with more prominent threats such as Lucario,Metagross, Flygon etc rising, there is more pressure on Diancie to the point where it becomes more of a burden to build around. Most of the Hazard removers in the tier can easily outstall Diamond Storms PP and freely remove hazards meaning its role as a rocker is slowly fading and being outclassed by the rising likes of Necrozma or Nidoqueen who do match up well into most removers. Diancie is still obviously good, it compresses the likes of Obstagoon and Incinaroar however outside that it is slowly falling.