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 that you would have Ditto stuck in the active were if you weren't in the lead at all and we're bricking throughout the game, which probably means that you've lost, at least in the standard format.