I believe that this is actually a good strategy. The main reason I say this is because if the pokémon you are trying to chain never calls for itself, you need to restore PP on that pokémon otherwise it will use Struggle and kill itself. Then with Harvest, the wild pokémon will never run out of PP. However, this is completely unnecessary for Pokémon that call for themselves some or all of the time because you can just KO the caller and the ally becomes the new caller. Hope I helped!
Side note: Harvest is always a hidden ability, so that is a downside. And Trevenant is the only pokémon that meets the moveset of Trick, Skill Swap, and Harvest, so you can't use Exeggutor.
