The Ash-Greninja is unpredictable, it could be good and bad. Also like DinoPokemon123 said, the show is awfully inconsistent. The second sentance I will try my best to answer. To me it means can alan win against Diantha, yes and no. Greninja is much faster which is why it actually 45% tired out Diantha's gardevoir, Alan could beat Diantha's gardevoir with charizard, but if that were to happen charizard would have to sweep hawlucha, tyrantrum, aurorus, gourgeist, and goodra without a scratch, or beat gardevoir without a scratch and then beat hawlucha, tyrantrum, aurorus, gourgeist, and goodra and take very little damage after every fight.