what about creating custom formulas? 3 types of damage:
strength-physical defense/attack
agility-agility? attack/defense//this will be like strength but not that "efficient", could give a bit of defense, or they will suck against any class :P
spirit-magic attack/defense.
agility should give a fraction of the attack given by the strength but a tiny bit more of defense, or the necessary to look fair, that way u can make a very balanced attack calculation(i dk how are the stats for pirates nor monk) so.
Ninja: High agility attack plus high attack/defense given from equipment, should be less efficient than trojan in melee figths.
Archer: High agility attack plus low-medium attack defense given from equipment, should be not very effective against any melee char(ninja, tro, warr), and better vs taos, not that much since equipment gives very poor attack
Trojan: will have a high attack in anyway, since all other classes have less melee potency than this one, except for warrs, but kinda weak vs taos obv.
Warrs: similar to trojans, but more defense than attack.
but this would require kinda lots of testing, but sounds pretty well :P...had this idea just a moment ago so it should be improved in case someone wanna use it

also reset stats would unequip the gears