Glasscannon is a global damage multiplier of +50% DMG and -50% Health.
Elemental Damage is part of the Weapon Damage Formula.
Multi Attack, depending on the Skill, is either an extra attack that does 50% of the original attacks damage or +50% damage for the original attack. in either case, this doesn’t affect the Damage on the Stat Page, but does affect the DPS.
I’ll show you the difference in what you want to know with Wizard Comet, because the damage mechanics are similar.
Comet does 100% Weapon DMG and 100% Weapon DMG AoE Explosion. Staff has APS 1.75.
only Glasscannon +50% and Multi Attack +4.
BWD
45 x (1 + (100/4)) x max(1 or 100/20)(max is the higher of the two numbers)
45 x (1 + 25) x max(1 or 5)
45 x 26 x 5 = 5850
everyone starts with Power Stat 5 at level 1. one Power Stat is 75 damage.
5850 + (75 x 5)
5850 + 375 = 6225
6225 x 1(Comet DMG) = 6225
6225 x 1.5(one Glasscannon) = 9337.5
9337.5 x 0.5(one Multi Attack) = 4668.75.
this part is 4 Seeking Comets each doing 4668.75 DMG. (decimals are usually dropped or rounded, not sure which)
DPS
9337 x 3(Multi Attack +4) x 1.75(APS) = 49.02k DPS. (does not include DMG from Comets explosion)
only Glasscannon +50%, Multi Attack +2, and +100% Shock.
BWD & Power Stat is the same as above
6225
6225 x 2(one +100% Shock) = 12,450
12,450 x 1.5(one Glasscannon) = 18,675
18675 x 0.5(one Multi Attack) = 9337.5
DPS
12,450 x 2(Multi Attack +2) x 1.75(APS) = 43.57k DPS
Glasscannon +50% with Multi Attack +4 does less damage but more DPS than Glasscannon +50% with Multi Attack +2 and +100% Shock, which does more damage but less DPS. this doesn’t include any other modifiers that you have on your Build.
hope this helps.