It debuffing is no excuse for it dealing less than half the damage of all other special weapons in the game while simultaneously requiring you to keep firing it to sustain the damage, saying that it's okay as it is is like saying it would be okay for Lumina to deal half the damage of all other primary weapons, simply because it buffs allies. A damage buff is needed as you might as well be equipping 2 primary weapons if you're doing anything with less than 6 people to benefit from the debuff.