So mastering a job gives you more stats/level, right?

And you can master a job without leveling much by killing just baby enemies right?

So I have this idea for a storymode game that involves doing basically nothing different during chapter 1, but starting as a thief to make it easier to win the first castle.

After that, you stay in Asiana, leveling up all the available class mastery without significant leveling.
You can head to Hallstatt to get the acrobat job as well.

Wait for your opponents to finish chapter or maybe even 4, then become a darkling. Your stats will be low, so even as a darkling you'll need to stay away from your opponents, but if you can work up the points to take over all cities on the map, you'll get an insane amount of exp after your transformation and your stat boosts will be idealized since you got the job masteries way earlier