Didn't want them to be overpowered, because the Flood Spores can take any Brute/Elite/Human, and if they take one of the stronger Brutes with 3000 ATK, then he'll 3500, as opposed to 4000, which would seriously be OP. XD I feel like such a nerd after saying that O_o.
PS. I love the quote in your sig. I'm stealing it for a Facebook status, if you don't mind.