I'm swimming around the continent on some tubby guy getting one shotted.
Did you beat act 3?
travel to the Endless Tower (it's a big tower in the SW) and complete the first 2 trials. You can try the 3rd but good luck. This will give you 2 grandiose catalysts to get 2 weps to 20.
Next we will go on Maelle's quest. Just go north of Endless tower to an even taller tower (Edit: it's shorter, I'm dumb), named The Reacher. This is a dungeon and you'll be completing it. This will give you a lot of levels. Likely 7-10 before the end. If you can't beat the boss yet, that's ok.
Next up is Frozen Heart, another dungeon near Monoco Trainstation. This area gives A LOT of Grandiose Catalysts. Keep upgrading and watch your damage soar.
After those two dungeons, you should be 70 with like 23-24 weapons. Now go to the Dark Shore in the South. It's where Expedition 33 met their end in ACT1. Time for payback. Big hand boys give a shit ton of EXP and guaranteed Grandiose Catalysts. Grind this area till your hearts content. Personally I grinded until 80 before I moved on.