To me, Hawkgirl is a character who is very passionate. I feel like passionate characters should gain meter slightly more quickly than level headed characters. Hawkgirl's meterburn moves also are not used so much for adding extra damage, but more-so for pummeling the opponent and getting up close. I feel like she could still be balanced if she had high meter gain to allow her to constantly be throwing out her meterburn charges. I think her character personality would flourish in this game because she would feel more like the fierce warrior constantly charging into battle.