I didn't think to post this earlier, but I wanted to add that you need to beat an entire 30 carnival trials in order to be rewarded with the job's Angel Whisper spell; since that's currently the job's only method of being able to raise someone in an instance, that makes it an extremely important spell to have in parties, especially in Blue Mage groups that are trying to earn titles or the difficult-to-acquire Morbol mount that you keep bringing up. It's incredibly helpful for multiple people to earn it as well since the cooldown for said spell has an incredibly high recast time, so each person with the spell unlocked realistically only gets to cast it once per battle, maybe twice if someone dies really early on.
The resurrection spell alone was incentive enough for me to figure out how to complete all the carnival trials, not just a few specific ones for certain job quests.