Similar to the "Broken Dagger" glitch from the first game, Dark Cloud 2 has a bug that lets you skip a huge amount of the weapon-leveling process. It takes a bit more work since tickets cost 40 Medals apiece, but you can start farming them around Chapter 3 and easily grab at least one or two tickets.
Basically, you just take any existing weapon and give it the exact name of another existing weapon (spacing and capitalization do count!), and it will become a copy of that weapon with base stats.
Watch Dark Cloud 2: Name Ticket Glitch from spoonshiro on www.twitch.tv
And if you're wondering what the exact names for the best weapons for each category are:
Max Right-handed weapon: LEGEND
Max Left-handed weapon: Supernova
Monica Right-handed weapon: Island King
Monica Left-handed weapon: Five-Star Armlet
Sadly it does not seem to work with Ridepod gear or any non-weapon items.