I think human and alien are balanced, both team will need teamplay, but alien will only need teamplay if human actuly use teamplay.
People who are saying that 3 humans>3 dretches are retard, since dretch is a sneaky class, you can't rush to a human and try to dodge his bullets, it only work with those who can't aim.
Now, there is someone who talked about human alway winning in scrim it's not true, as I said before, alien will need to use teamplay too, but they can't fit 2 goons in a small room, so the only way you play as a team, is to swap, 1 goon attack, go back and the next one take his place.
Someone also said something about Human with skills>Alien with skills, But how can the Alien be skilled and still lose? since they have the advantage when human are still S1, when human hit S2, it's a little bit harder, but if alien defend their base, and use the booster, they will probably be able to hit S3, and then push the humans back to their base.
Sorry for my bad english, I will probably explain a little bit more back to home