IMO, small numbers always equals not OP, at least when they are irreplacable.
You have 100 dudes with deathrays. I have 10,000 with sticks. I can get more. You can't.
Balances itself out.
EDIT: And really, should be get too worried about balance? We're talking about a galaxy full of dominant lifeforms, some of which have headstarts on others, etc. Things shouldn't be equal to a degree. I think a bit of disparity makes for better RP, personally.