I don't quite understand your logic, how are you being penalized on new characters? Tab 4 is going to cost you a million and have requirement of 50 no mater what. Buying the unlock hasn't affected your new toons in anyway except that they got two free bank tabs to begin with. I waited until all 7 of my toons had 2 unlocks already to get the best value. I'll have the expensive slots paid for on my existing characters and the cheap ones on the new ones. So its a better value the more characters you have when using the unlock. However, in noway are you being penalized on your new character, they just don't get as great as a deal. You can always buy individual cargos to top off your new characters.
Disclaimer I only paid 700k credits for my two unlocks