I always believed that Physic Pokémon could communicate telepathically with no issue, but then Rajin had Yvelta communicate with both human and Pokémon, telepathically. That seems like a huge leap from what I believed to be the case. Maybe a Legendary Pokémon can communicate with other Pokémon but I think that a Physic link between human and Pokémon should be limited to just a Physic type. But maybe for Rajin's case, Meloetta could act like a pylon to communicate that Physic message because Mel is a powerful Physic type. A less powerful Physic would not be able to relay that information. But that's just my two pence.