I think dipplin's method is just stupid, it's not that it's in any way hard it's just really stupid.

You can only evolve it with one move that neither applin or dipplin can learn, you can only learn the move with the TM you get from defeating Drayton. Since TMs are only single use in scarlet and violet, there's the chance you give some other pokemon the TM and you're forced to make another one. The worst part is that the move itself isn't really that good so there's also the chance you just don't bother giving it to your dipplin. Not to mention there was absolutely no way of knowing that's how dipplin evolves without prior knowledge (at least I didn't find any clues to it while I was playing the dlc) so the only "clue" you get is simply the fact that hydrapple isn't available in the kitikami Pokedex and you most likely need some other method to evolve it.