Well Sir, you did see the damage values right? An additional slot (Effective) and you more than double the damage in ~80% of the cases? And still deal ~20% more damage if effective coincides with Greatly Resist?
Either you didn’t understand the matter or you are trolling 
Well, it’s still in the Wiki (Affixes | DungeonQuest Wiki | Fandom) like that but that’s wrong. It is exactly like I described it…
Because with the whole Ignore Resist/Weaken/Effective matter many people post things they heard somewhere but never verified that are just wrong. 
The only thing I did not quite completely understand is how the internal monster resistances are calculated. But how Weaken etc. work is solid.