You still have to fit it all in the moveslot, if you build fin to just kill those things it will probably struggle against other stuff that would die to more common fin sets, which in return will handle fin with ease. It would just be better to grab a raging bolt or smth to kill dozo and mola rather than make fin the mola/dozo killerLike I said before, Palafin’s movepool is pretty big (with Encore shutting Dozo down pretty badly and Taunt bullying Alo) and it even has 106 SpA to take advantage of more niche options. Grass Knot is pretty much a Dozo killing move and Alo doesn’t like having to eat that either. Whatever Palafin feels like checking/countering for the day, it can put on a move to do so.
Despite that, you do raise some good points