There's no reasoning to try to say that Ditto Prism is a bad card purely due to it's weakness to Buzzwole. If it were to be 70 HP then it would be understandable. Buzzwole is almost always going to get a Strong Energy or Diancie in play, so his weakness is really invalidated. The only situation...
It functions like Shaymin, in which you can't activate it's ability after you use it initially. You can use it's ability multiple times if you bench more than one though.