You don't even need maxed out potions for that. 2 desperation potions are enough.
use a desperation potion to kill off one of your useless characters
have enough voltage to give Tsubasa +2 atk on low HP
use a desperation potion and an attack potion
now all of your hits deal 4 damage, most enemies have 4-8 HP
add +1 attack when you have enough voltage on top
I mean shit maxing out everything will just give you +2 atk, it doesn't really matter that much if you deal 5 damage or 7 at that point, the overpowered part is having a no fatigue areal attack