[Well that's... not what he wanted to hear. His simple little worldview is taking damage. Animals are just supposed to follow their instincts. Stuff like this is for humans only, right?]

Have you tried getting him to not do it as much? Maybe tell him everyone already knows he's strong enough to beat weak Pokémon, so he should be proving his strength by trying to beat the ones who are as strong as him? That would make him look stronger than going after weak Pokémon, since anyone could do that.

[He clearly doesn't like suggesting behaviour modification, but it's better than letting a Pokémon act like an evil human, right?]