How did the Order and Admiralty Hall come to wield so much power?
Evil begins when those of good will sit back and do nothing. The Order on Vulcan thrived because it seemed to be cooperating with T’Pau in expressing her distaste for and discomfort with humans. She was not as bigoted as they, nor was she ignorant of their nature. But they managed to use her by not seeming like they did. In fact, T’Pau thought she was in a way containing their activities. As for The Hall, it just took power, a little at a time, and no one said no. By the time anyone could object, their power was quite real.