Basically this is a suggestion for the amount of class exp you gain from an enemy (that is not in a dungeon) to scale based on the difference between your current class level, and the enemy's level. Since some dungeons already give a lot of class exp, this shouldn't really cause any balancing issues, since your guild members can already help you level different classes up quickly by killing the enemies inside. For example a level 60 enemy on the field shouldn't barely fill your exp bar any faster than level 30 enemies when your class level is level 30. Yes there are already items to boost your exp gain, but like I said using those items in a dungeon while your guild kills enemies can be much more broken.
It doesn't even have to give you that much more exp depending on the level difference, I just think there should be some kind of class level scaling to make it easier to level up the classes you haven't used. Yes up until class level 20 is an instant level, but it starts to slow down a lot once you reach that point. Since leveling other classes makes you more powerful in general (from titles and skills) it would make sense to be faster to level up other classes when you get to a high enough level. Yes you can level other classes up fast from quests too, but I think we should just have more options in how we choose to level them up.