If you grinded too high, go to the Zeklaus Desert, find the de-level trap panel, and have your characters repeatedly step on it. It will de-level you so you're back to a manageable level. Be careful with stats as level up and down are impacted by the job you are.
I had no clue you could De-Level lol. That's wild and pretty cool, thanks for letting me know
Yes, this is how you min/max your character stats (assuming you're not modding them).
You level up with a class like Ninja (high speed growth), then de-level as a class like bard (overall low stat growth).
To help the level down you defeat all but one enemy, then use the knight skills to rend speed and power on that enemy so they only get a turn rarely.