Balancing is not easy, I understand that, it is frustrating to receive that kind of feedback, without any suggestion on potential methods to achieve it.

Methodology: I suggest setting up an auto script with 3 designated variables for each character, letting their AI run an ideal damage per second skill and attack rotation on an invincible target dummy for around 10 minutes each per test. Track the average damage per second of each variable. Then adjusting the characters core stats as needed. Rerun the scripts to test dps outputs and tweak again as needed.

Variables: 1: Max lvl, no wedges. 2: Max lvl with +5 purple wedges using the ideal wedges for that character for a DPS main play build. 3: Max lvl with +10 gold wedges. This lets you balance a crossed tiers. Run each variable for each character for 10 minutes exactly on the same training dummy approximately 5 times, then average the dps results.

The finale: Decide whether you want the character to be weapon focused, or skill focused.

Weapon Focused characters (Outsider, Fina, Khezou, etc) should have their base attack raised until their dps output is roughly equal to or within a 10% range roughly of the current highest dps characters.

Skill Focused characters should have their skill modifiers for their skills raised until their dps output is roughly equal to or within 10% range roughly of the current highest dps characters. For example: Nifles skill modifiers are around 6 thousand, while Tabethes are around 100.