Currently Magic Potency is the stat that allows for a user to be more effective with casting spells. It is essentially something along the lines of Attack Power for Physical Attacks.
In general though Melee weapons have a limit to how high their Magic Potency goes, a huge majority of them never see above 5. While most Mage Weapon Classes see 50+ on their Magic Potency.
As a result to be a decent magic user you are limited to Mage Weapon Classes only, so properly filling the roles of a Hybrid Job like Paladin, Dark Knight, White Monk, Holy Dragoon are very difficult.
To rectify this, a series of weapons needs to be released that gives access to Higher Magic Potency at the expensive of total Attack Power or a negative to Physical Accuracy.
These would be similar to the Rune Weapons from FFXI, They were Melee weapons most/all magic Jobs or Hybrids could use and would use the Mages stats (and MP) to pay for extra damage or other hidden side effects.
I Feel these types of weapons would help allow some players to properly portray Hybrid Job/Class Combinations.
Examples:
Current:
Banneret Lance Rank 48
Attack: 171
Accuracy: 133
Critical Hit Rate: 144
Parrying: 144
Magic Potency: 14
Magic Accuracy: 118
Damage Type:
Piercing: 100%
A crafter can imbue it with Magical Ability
Holy Banneret Lance Rank 48
Attack: 90
Accuracy: 105
Critical Hit Rate: 144
Parrying: 80
Magic Accuracy: 118
Magic Potency: 126
Damage Type:
Piercing: 80%
Fire: 10%
Wind: 10%