If it really only adds a single extra attack, then there's literally zero reason to ever bother using a weapon that has 30% less or more attack power over your primary, even at 100% zing. Not only will it do overall less damage, it also becomes mana inefficient.
Also, despite the game being pretty easy, I'd suggest unmemorizing all but one or two skills from the party members that are in your group, but that you rarely (if ever) manually control. It stops them from wasting so much mana on stupid shit all of the time.
Yeah it's more annoying to constantly remember to switch weapons for a special attack when everything's pretty easy to begin with. It would be better if each character could use different weapon types that change how they fight but using 3 swords similar in attack strength is pointless.