The Oni Approach!
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Frank began to consider why did he required more levels to max his Job out, amidst the many things that could be, he imagined that it could be something to do with his own power level growing bigger, he required more levels to traverse the strength required to reach the next progression wall, which was the level cap.
Although he was happy by just waiting for the levels to reach max level, which didn't take that much time honestly, he still felt like going into a Dungeon could hasten the process. However, he had already gone into the dungeon and was actually inside Orb's Dungeon using his new Abyssal Chaos Clones made out of his Divinity and pieces of his soul, which could gain EXP for him. But even then, he was still gaining EXP at a slow pace.