Here's a hint -- take the 'level 70' side quest on your level 80 main, complete the quest as a level 80 main, and turn it in as your alternate job. That way you can take out the mobs with an appropriately leveled job and still turn in as the lower level job.

As an aside, all side quests in this expansion are labeled as 'level 70' regardless of the area you get them in.