It's quite possible that the Scions have specific actions in their toolkits, so just because Thancred is a GNB it doesn't mean he has access to all the actions like we the player would have if we were playing that job. Y'shtola has quite a few aoes but those are part of her rotation, everyone else just focuses on taking down one target at a time. As tedious as Trusts are (after MSQ), we were warned that these runs would take longer than using the Duty Finder so it's not intended to be a replacement of a team with actual players. I don't think the Squadrons use any or many aoes either and they are inferior to Trusts, but the AI had come a long way so maybe in 6.0 they'll use aoes but for now doesn't seem to be a big deal.

(Challenge Log entries offering bonus exp to your trusts for doing X number of runs could be a nice little thing though....).