Yes, Cham, giving DPS adds to the total raid DPS. That's already calculated. But adding VoG AND constant cursing on the mobs was too much. Curses could be chained to increase the DPS expontially. VoG can't.
The fact is, enchanters were giving the raid too much DPS with curses. (We're talking about raids here. If you note WIz's post, he made an analogy that "The equivalent would be giving SKs rogue DPS on raid mobs". RAID mobs.)
Adding another enchanter to the raid meant another several ticks of crits, which is MORE dps than you would get from adding another wizard to the raid. So yes, enchanters were giving more total raid DPS than wizards. Granted, if you had a raid entirely of enchanters, it wouldn't be... but that's not happening anytime soon.