What I want to know is why Maechen didn't do anything? From X-2, we know he was around at Yunalesca's time. He spends a fair bit of time chatting to you at Gagazet, detailing the entire history of the Machina War, and I'm sure he would have known of or at least suspected the existence of Yu-Yevon. Being unsent, he could have easily got close enough to Sin to launch an assault on YY. Plus, he's not exactly defenseless; X-2 implies that he's a black mage.