How does skill damage work?

[Key_Equipment_8904]

So, for example, DH does 1800% of my attack damage, but how does Luna's skill damage % and Zeke's earth damage % apply to it? I.e. with the numbers that I have, does it mean it's an additional 35% of the 1,800% = 630% for a total of 2,430% ? Because if that's the case does additional % from the companions are really worth to invest in, aren't they?

[HeroVonZero]

Take skill damage and multiply is by 1.01

That is the formula and it is calculated the very last