As many said, IS' ACs are heavier and bulkier (take more tonnage and space), Clan' ACs should have some drawback.....i do agree, but the current state of cAC make it sort of a placeholder (i do rarely use cAC10 on some hot build since it is cooler than UAC10, though), the current state of clan is that it lack single shot ballistic guns other than the gauss, the balance could be maintained IMO, by adjusting the numbers, and differentiate the IS and the clan, for example,
Clans' are lighter and taking less slots (current state);
IS' ACs' cooldown is ~15% shorter than clan;
IS' ACs' generate ~10% less heat than clan;
Clan' ACs' range are ~4% longer than IS';
I knows PGI wont listen.......but it is my dream
