That's BS. There's no source state that an old god is more powerful than a titan. In the Ordering of Azeroth which is in game book it was stated that the titans were actually outnumbered by the endless amount of faceless one and elemental lord armies. "combined might of them couldn't stop the mighty titans". A titan fell but all old gods were defeated and imprisioned with one killed. The titans would have killed all if not for annoying effect Ysharrj caused after his death.