Idea on how to achieve perfect balance: add poltergeists! Here’s how it would work:
When playing as a human or an alien you get polterpoints just for playing.
In future games, you can opt to spend some of those points to become a poltergeist, and every game should have one or two poltergeist slots depending on how many players there are. Poltergeists should essentially be a third team of sorts.
Poltergeists are able to help either team, for example by granting players a temporary ectoplasmic shield, revealing some of the enemy team’s private messages, moving structures a limited distance to weaken the enemy base or help strengthen their own and so on.
When the game ends, the poltergeists get bonus points (which are separate from polterpoints) depending on how well they have accomplished their main goals: to prolong the game (1), ensure that (2) both teams take as much damage as possible, and that (3) both teams take comparable amounts of damage. They can then spend those when playing as a human or an alien to get some advantages.