Almost perfectly correct.
All the supported skills listed on the 6p bonus will be buffed by 9000% or 90x.
I didn’t state something correctly previously. I got mixed up with Necrosis and Wall of Death, thinking they were the same skill. It’s been a little while since I played HT, apologies.
To calculate Wall of Death’s buffed damage, just multiply the tooltip number on the skill/rune by 90. Please disregard all previous info, I missed a decimal, so the damage is actualy 10x what I previously stated.
Ahem… ok so the correct info…
Necrosis is a DoT as you said. It is not buffed by the set, it is just a flat 3000% weapon damage. You can apply this with any of the listed skills in the 2p bonus.
All Necrosis will do is tick its damage, slow the affected monsters and begin the 10 second timer for your 60% DR buff.
Now, only Wall of Death will activate your 9000% damage buff for 15 seconds for all the listed skills, it’s not connected to Necrosis other than it being able to apply it.
So you can safely ignore the Necrosis damage at higher GR’s. Your other abilities will be doing 100+ times the damage after factoring in supporting legendaries.
So in summary…
Casting Wall of Death:
Will activate your 6p (9000% or 90x) damage buff for 15 seconds whenever you cast it, and will also apply Necrosis (for a flat 3000% WD p/second + slow) activating the DR buff when it hits a monster.
Any listed skill will activate the Necrosis/DR buff… so if your Gargantuan is hitting stuff, it should pretty much be up anyway.
Sorry for the Wall of Text, but I didn’t want to leave anything out.
Hope it helps.