Its pretty obvious. Calculator is your reward for gathering all the magic you can in the game then skilling up the slowest class in the game. Are they very overpowered ? Yes, but not everyone is gonna take the time to work up a master calculator and its the reward to those who do. Lets face, it you sit back and get a Calculator all the magic and his class mastered, you are gonna beat any part of the rest of the game without any effort due to your efforts in powering yourself up.

That said, Math Skill is no more imbalancing than Orlandu spamming Night Sword with Blade Grasp and MagicD/Defense Up skills equipped, who ends up being nearly unkillable, or a 1 hp Beowulf running around hitting everything instantly for 600+ damage.

Personally, I never liked Math Skill and never used it much. Short of equipping your entire group with a specific Absorb Element armor, its too tedious to me to check and recheck every spell I want to use. I'd rather just use a Summoner or Time Mage and know where my spell limitations are