Heroes & Villains not always available even with enough Battle Points

This is actually not a bug, it's because there are limits on how many heroes are available in certain phases.  

I've always wondered about SA, though, that the light side always gets 3 hero ships and the dark side only gets 2.  Given the power and resilience of the MF in its 3 forms, I've always wondered if this imbalance was intentional or a glitch that has just been ignored for half a year.