Tests were done on Spindiggles, there were no resists, and everything was combo'd

First gear set, 261 INT & 451 M.Pot


Parse

Thunder average 593.47
Thundara average 1104.94
Thundaga average 1314.90

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Second gear set, 261 INT & 494 M.Pot


Parse

Thunder average 643.47 8% increase
Thundara average 1131.79 3% increase
Thundaga average 1419.67 8% increase


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Third gear set, 362 INT & 489 M.Pot


Parse

Thunder average 726.64 12% increase
Thundara average 1487.89 31% increase
Thundaga average 1661.80 17% increase





Conclusions:
  • Looking at third parser, Thundara (Thundara also have 'increased damage' effect in the combo bonus) received the major boost from INT, while receiving next to nothing from magic potency. This leads me to believe combo's damage modifier/formula highly relies on your stats especially the one that has 'increased damage' bonus.
  • 40 extra magic potency which comes from Hexa Mask and Ifrit's Cudgel increased a very little amount in terms of damage, will devs look into this? because this would render Ifrit's Cudgel usefulness next to none when a single INT Lightning Brand will outdamage it far beyond.

p.s stats does work. (INT at least :P)