Yeah, Brains got a huge boost in the tribe switch. They teased it in the opening segment, night of the tribal before the switch, when Spenser said "All that's between us and final 3 is two whole tribes". It could actually happen.
The odds of all 3 ending up on the same team after the switch are really about 50/50. Elsewhere people are saying it's rigged but it's entirely possible. No matter how they pick, at least 2 of the 3 are going to be on the same tribe. So it's just a matter of the third picking the same color as the other two, nearly 50/50 (actually with 14 people, 2 having picked orange, it was 5/12, slightly better than 40/60, close enough).