Lower cast time is like comparing fast cast with instant cast of RO
without much excessive damage either. Melee attacks like Ninjas usually do more damage without any charge time. Spells need cast time no matter how they are looked at, not to mention damage goes down if the opponent has low faith (melee attacks do not obey the same rule for low brave though.)
Calculator's ability will make magic instant cast, however, which is how magics are usually used.
Summons are the only one justified (and yes, with the time mage's support) to Namin? to be deemed worthy of using, because the low level summons are reasonably fast with a large aoe that normal black magic will not reach until the Lv 4 spells (with their amazing... 10 speed? Shiva/Ramuh/Ifrit has like 30 or 35 and not too bad in damage either, without friendly fire)
Namin? went with thief for Ninja. Thief gives the most speed boost, which is the only stats the Ninja needs. Throw ability's damage depends on the item thrown and the Ninja's speed, not strength. Matters not for Namin? if she got no weapons, as long as she can move 3 times for everyone 1 of the opponents and deal all damage by throwing those 50 bucks shuriken ^_^ By the time throw is not doing enough damage through common items, the Ninja swords are available already.
Namin? likes Knights to be a better transition to Lancer instead~
Either way, Namin? will imagine that healing is probably an issue, as her first play through has the same problem. Rely on items, and less on white magic. Hated the unreliability of white magic, and how raise will miss... Mustadio makes a great chemist for obvious reasons, and Namin? likes to rely on chemist far more than white mage (Namin? only learned cure, cure2, raise, and holy. Raise2 and Reraise are close candidates, but usually not needed by that point of game because the enemy gets more and more a joke...)
To be honest, Namin? finds early parts of FFT to be far more challenging than the later part of the game... In a match of fighter vs fighter, not much strategy to win =/