Quote Originally Posted by gottesurteil View Post
Erm, kinda yes/no? Yes, the eidolons stack, but the thing is Character Atk vs elemental Atk are calculated separately. Elemental attack (like on apocalypse) becomes FAR more useful than character atk with your weapons grid. There's a post that talks about the actual math (with proofs), but basically take it like this: elemental attack is better. It actually becomes worth MORE as your weapons grid rises. Almost exponentially more.
I have a calculator for this that allows you to input arbitrary character attack and elemental attack bonuses, and even accounts for burst combo bonuses and teams with off-element kamihime. So you can compare relative damage for two potential teams using your personal assault skill and eidolons.

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Quote Originally Posted by Aidoru View Post
Element Atk =/= Character Element Atk.

Damage formula
( 1 + a + b ) * ( 1 + c ) = x
a = character type boost from eidolons
b = boost from weapon skills
c = element type boost from eidolons

Let's pretend you have 100% damage boost from your weapons.

With 40% character boost (Crom)
(1 + .4 + 1) * (1 + 0)
2.4 * 1 = 2.4
240% damage

With 40% element boost (Apocalypse)
(1 + 0 + 1) * (1 + .4)
2 * 1.4 = 2.8
280% damage

You loss 40% damage using Crom over Apocalypse and that value only gets wider the more you level your weapon skill.
That's actually a 14% damage loss using your numbers. You forgot to divide the 0.4 difference by 2.8.