If you wanna bump based on BaB that means every monster gets those advantages. In fact You've probably just handed demi-god-hood to every high level monster of the dragon, Monstrous humanoid, and outsider types.
Casters get abilities far outside the basic skeleton, in exchange their basic skeleton is weakened, but there is a difference between a person with brittle bones, and a person with no femurs.
Your justification is highly flawed, sure a mage who is doing well rarely if ever makes use of their BaB. The same can be said of commoners, aristocrats, experts, and some rogues. By your logic these characters should not receive BAB either.
Furthermore your idea to had out extra attacks, or longer steps to the high bab classes doesn't address the core issue holding those classes back. THe full attack action. This is your enemy, it forces the fighter to choose every round whether to make a singe attack and cover some ground, or to do something akin to real damage and go nowhere. Longer five-foot steps combat this, but do not solve it. The prevalence of charger, and even pouncer builds is oft quoted as a solution, but many players dislike using the same strategy every single turn.
If you really wanna help the melee classes, ditch the full attack action and iterative attacks, instead of getting extra attacks at bab 6, 11, and 16, make their attacks deal additional damage equal to the weapon's base damage die. So a dual wielding ranger at level 6, with twin short swords hits for 2d6 on each blade. You'd have to remake a few feats and overhaul the two-weapon fighting rules a bit, (i'd be more than happy to help), but that should start making it more attractive and fun to play a warrior type, and make them harder for the monsters to ignore.