Make sure you're actively replacing your pawns. They do not level up with you. Honestly, get a high level pawn off a buddy and be done with it if you're really having trouble. The exp penalty is garbage if your pawn is 2 shotting stuff for you. Personally, I avoided mage based classes like mystic knight, but I've read that they are crack in a tin can. I still prefer my sexy assassin.
If anything, level up vocations just for the assortment of abilities. Autonomy is awesome later on when running solo isn't scary, and couple it with other stat boosters and you get ludicrous damage boosts. The game does the math in a newfangled way, rather than a boost of 10% and 20% giving you 30%, it boosts your stat first by 10%, then boosts that result by the next bonus of 20%, essentially giving you a much higher bonus. Autonomy, clout, vehemence, and bloodlust give a ludicrous boost to my damage when I'm alone at night, multiplying my base damage by almost 5 times. Autonomy and Bloodlust also boost magic, so it's great for mystic knights. Both are assassin skills iirc. If you want a good warrior, you could always take my pawn. He's big and bloated, but he hits like a dump truck and is level 128 I think now.