This is just my opinion and prediction:Everyone had a chance - they had the early game to make a good impression, then a chance to win the ' advantage' challenge. Saanapu won, they picked the people who had proven themselves desirable, and now they have the advantage.
No, it's completely skewed the game. One challenge shouldn't do that. Not for this long. There is no way that the blue alliance doesn't take out Vavau when they merge. That one competition set up the majority of the game, I'm guessing well into post merge, maybe another 6 eliminations.
Even a good player like Craig won't have a chance against poor players like Lee because they will target him due to his strength. No telling what allies will reform because they've been with their second tribe longer.
I don't understand why the producers would do all that initial movement and then keep things static.