His quick decision to join the brain proves that his only ambition was power. He wanted to be on the winning side. When he saw his goals as impossible to achieve because you no longer needed him, he sacrificed his own freedom for power again. That being said, they could have built it up better by making his true ambitions more transparent when you've been nothing but distrusting and hostile towards him from the beginning. They could 100% make his rant longer after you decide to free Orpheus and make his manipulations worse if you've been trusting towards him. I never trusted them from the start so it wasn't much of a shock when he said, "Aight, fuck this I'm out."
