Do you aim higher whale ship stages? If yes, Dahlia is better, if not, Ivy is enough.

Only the girl in fight have their ability triggered. Nevermind if abilities are triggered after team 4. If you use more than 4 teams, you're already dead. Last teams are rarely good (or if they're good, you don't even need them) and they are here only to get more TP for the ship.

Whale Ship is serious business.