It only doubles it if you have low M.atk, the number of hits is the same, you only get base damage pumps.
If you consider only a 7 rank gaming, you can go Necro 2, You’d have nice squishy minions and +500~600 damage per hit from 5 levels of flesh skills.
Warlock has 25 hits on Theurge, best AoE ever for Linked mobs when using HK, 5 hit per mob killed from Invocation. That at circle 1, this game will not stop at rank 7, you can barely imagine how good rank 7 wizard classes actually scale when you put them under the right skill setup.

