Job Leveling up in Final Fantasy 3 without it being boring

As the title says.

Edit: Apparently, you dont need to force Class job grinding on, Onion Knight. You do need to get Job level 99 for Black Belt if you want to Level up with 9999 HP with the quick way of beating the game on perfection, of hitting respawining "Kum Kum" enemy spawned from "Bluck" enemies.

But i had low class job levels of Onion Knights, with normal level 97. And i beat it, tricky but doable.