Just did another run with a different build (I managed to bring peace as an Arland princess while romancing Clarmont) as a Jiyel scholar and I can definitely confirm that there's some hidden stat needed in order to get the option to aim for peace to pop up. I tried messing around with the choices for when you talk with Sarya on the guide I posted the link to and the option for peace didn't pop up. I'm guessing it has to do with persuasion or manipulation, or maybe people? I would need to look back on my saves and compare my stats.