[Taqwus]

And you spent gold to get those other mages, and to pay them to run around and find sites, and to keep them on the battlefield to cast the battle magic that other paths place far greater reliance on. You also spent money on mages to research spells scattered in up to seven other schools -- and this is more expensive now, since research has been slowed, while blood is much more unified.

Oh, and blood nations will have far fewer expensive mages dying of old age than your average human nation, once they research Boots of Youth.