Using optimise will equip the weapons with the highest attack power and the armour with the highest physical defence. Most of the time, this is not the case. In FF2 you want to be dual-wielding weapons of choice for most of the game (it's easy enough to simply change your character's specialised weapon to whatever the strongest is e.g. the Axes from Mystidia), and you want to achieve maximum evasion. This is achieved through shields early on and lighter armours later. Anything that gives an Agility boost (Black Garb, Thieves Gloves) is also highly recommended. In this sense, using optimise doesn't mean you'll be optimised. Genji Armour, if you have a full set, will automatically be equipped with optimise, and happens to be the worst set of armour in the game.