[dappa]

When I cleared the game I had leon on level 10 for most of his spells. I couldn't be bothered to get em to level 16. But If you go to pandemonium and get him to attack enemies in the secret room where the masamune blade is I have noticed his proficiency level goes up faster. Thats what I always do for the fourth character.

As for getting the characters levels up fast all I did was cancel an action around 100 times to advance a level. So you can say within 16 battles you can maximise a stat or spell. Once you go past level 10 on a spell you roughly need to start cancelling around 150+ times. It can be hard on your hands as they will start aching after awhile.