Though easier metal slime battles would be welcome, Dragon Quest IX's levelling system is far from broken.
Yet, based on a suggestion from the GameFAQs forums my level grinding just got faster.
Reducing my party to two members gives both far more experience than they'd get as members of a four person party.
Nonetheless, the game's experience divvying is weird. It doesn't give more experience to the lower level character. Instead, the lion's share of experience goes to the party member who does more. So Nizk, my main character, is going to be a few levels above 45 when my grinding's done.
At least the Bowhole's Liquid Metal Slimes give about 20,000 experience per party member. It's just a matter of defeating them with only two. A feat that'll be all the trickier while bringing up my Mage's level.