For leveling, use fates, levequests, daily hunt bills, weekly challenge log. If your role isn't needed in DF parties, then you can not do it and level through those other methods, mainly fates. Disproportionate queue times can't really be fixed with the way the game uses a Tank/Heal/DPS composition requirement.

Maybe the next time they do an FF mmo, they won't do these holy trinity roles and jobs can be more unique instead of fitting into templates, like how Astrologian had to be similar to White Mage to fit the requirements of a healer, limiting what could be done with its card support buffs and offensive spells.