I'll bide my time first. I need to educate myself with the algo first.
If you abuse the useless Genji Glove+Offering+dual Tempest+Quick, on average, 8 Wind Slashes would occur max, which is worse than the 5 Ultimas if you do a Gem Box+Quick abuse (Quin-Ultima) attack.
Wind Slash doesn't ignore magic defense.. the initial power is 48, though I don't think it is affected by the multitarget power reduction modifier (of 1/2)
Ultima ignores magic defense, initial power is 150, and is always affected by the multitarget power reduction modifier.
Even if the monster had 0 magic defense, the spell power of Wind Slash is still weaker than a split Ultima of 75, Wind Slash being 48/75 = 64% weaker on same magic power and level. This gets worse over time based on obvious math.
In sum, Wind Slash on average is never going to be as powerful as Ultima, but I could bother to take a look at optimal level+magic power conditions for Wind Slash... but that would require a lot of work to even remotely match Ultima (I'd have to check how much it would take to even make them a fair comparison).
I mean, the magic defense algo is primarily magic defense/255 and once that is reached, Wind Slash is virtually irrelevent. That doesn't even factor in the elemental property, although Ultima is Runicable... I'd hazard to say that there are more enemies resistant to that elemental than the enemies that have the Runic ability.
It doesn't help if Wind Slash is used 8x if magic defense = 254 in the first place.
Edit: To expand on a related idea..
Quin-Ultima is 5x75 (assuming always split) = 375 (before multiplying level and magic power)
Hex-Tempest is 16x48 (since split is not applied) = 768 (before multiplier level and magic power)
So, if all goes perfectly, Hex-Tempest is better, BUT requires so much luck to cause, ebmid is delusional.
So, these things hurt Tempest's potential, in the order of things are likely to occur:
1) 16 (8 on average) Wind Slashes needs a prayer to occur
2) The chances of Ultima killing one or more of its targets to eventually remove the Split damage modifier, which starts to favor Ultima more
3) Enemy Magic Defense > 0, Ultima cuts through any magic defense like butter
Things that can't be compared against, because of the number of monsters that expose it, but still notable:
1) Runic vs Ultima - too few enemies expose this, and you can control your own Runic command too
2) Wind elemental - you can work around it somewhat (requires Tools -> Debilitator which has a 1 of 8 chance of doing what you want it to do, but is single targeted and won't work against monsters that rotate elemental weakness)
Let's not forget you could do better with Cyan than giving him very little evade or magic evade to survive. The fucking Retainer would rape Cyan on Tradeoff.
What hasn't really been considered...
The number of attacks an Oct-Tempest (using average here) deals is far more than Quin-Ultima, but requires some consideration. Quin-Ultima has the early edge by design because of the magic defense and high magic power (150 is a lot after all). Ultima plateaus pretty quickly, and Wind Slash/Tempest requires a lot of level ups and Magic Power boosts (which is terrible for the low level game player).
Note: I'm more of a Merton/Meltdown guy, since that provides far more benefits for me than Ultima or Tempest/Wind Slash under most instances.
