C'Thun is probably more powerful than any current Dragon though. That mega-blastmage effect is immediately effective in ways that Alex, Nefarian and Ysera are not.
If there really are 16 cards that synergize with C'Thun, we should be able to tech around any real weaknesses - where as the Dragon decks completely rely on synergy and having a dragon in your hand.
The C'Thun effect makes me understand why they have to nerf Alexstrasza. I can see a Warlock doing Twisted Nether > Dr. 9 > C'Thun KO.