I have to agree with DalzK. When Rook camps a portal flag, you're screwed.
And if the other team having Giants means you've lost, you've played poorly. Most of the time, it's not game-deciding just having Giants.
I found a good health-stacked Oak player with HoL to be completely impossible to kill in 2v1. It's not like we fed him or anything. In fact, we had more kills, map control, and never had a problem with Oak's ally. Then Oak got HoL.
He hit 6K health mid-game. Late-game, even with full burst damage from Sedna and UB, it was about six seconds to lop off 5000 or so health, six seconds more and he was back at full health, and another six seconds before we could even worry him some more. 12 seconds of PvP combat with absolutely nothing to show for it and another six before we would, and by then his ally has been in the fight for at least six seconds.
It was really frustrating to simply not ever have a possibility of killing him. We got close a few times, but even with Silence, his health was so high and the player good enough that he could always make it back to base or his ally if we were able to drive him off. We would be in no condition to fight after that, and so Oak would come back out and immediately drive us off. Trying to fight 2v2 was just pointless. His ally stacked health and had HoL as well.