Heavensward Spoilers -
Why would Ser Aymeric and House Fortemps immediately believe the truth about the Holy See? 1000 years of the See feeding Ishgard bullshit about the Dragonsong War and what caused it, and a story from a newcomer (although famous) to the city, who obtained the info from the opposing side convinces them otherwise? Not even a "You've been fooled by the dragons' illusions and trickery." or "You expect me to believe our protectors have been lying to us since the beginning?"? Just... "Ok, Warrior of Light. I'm going to talk to the Archbishop about this. If I don't come back, attack the Vault and rescue me." I get that the characters believe executing Aymeric would've shown the true colours of the Holy See, but how many people wouldn't just say "I can't believe Aymeric was a heretic."? 1000 years of religious crap should show a lot more in the city than what was shown.