Your Leather Mastery adds very little of each stat. Gunner masteries give more attack speed, Rangers get more crit, and the Light Armor users get so much more strength that it makes BMages still look puny. Your intelligence and and MP recovery is also a downgrade from the generic Mage's Cloth Mastery.
Let's not forget that despite Leather has higher defenses than Cloth and BMages have a slightly more efficient Mana Shield, Leather is still mediocre. BMages are more likely to take damage more often too, since their fighting style forces them to be direct and planted to the ground.
BMages are fast; I'll give you that. However, they statistically don't accel in any category because of how spread out their mastery bonuses are.