In the beginning cut scene for the quest Wrath of the Titan, Y'shtola describes the last time the Primal was summoned. In describing its defeat, she states:

"There but for the grace of the Navigator were the mercenaries Merlwyb hired able to fend them off."

The phrase "there but for the grace of God (or the Navigator, in this case)" is used to negate the action that follows. Unless I'm very much misreading things, the sentence above is saying that the Company of Heroes was unable to fend off Titan and Leviathan in their last encounter.