People were right about DQ7, the game picks up a ton after unlocking Classes.
Funny thing is, they tried to prevent class grinding by using an area level cap on each area (let's say you're level 20 and the area's level cap you're in right now is level 15, this means your classes won't get XP in that area), but there's a way around this.
There's a special area called Slimetree Forest, where the only monsters are the basic Slime. In the forest, the level cap is 20, so if you're lower than that (which you most likely are right after unlocking Classes), you can just keep grinding there because Slimes give so little XP you'll max out classes before reaching level 20.
Now if you'll excuse me, imma go break the game (not really).