Think about it, Seraphim are an alien race, they shouldn't be a playable faction at all. Gameplay wise, there is nothing unique about them, they are simply a mish mash of the other three faction's qualities. They have the tankiness of the UEF (think t1 tank, Illshavoh), the shields and fragile units of the Aeon (such as the sniper bots for fragile units) and the stealth of the Cybran (eg, the OP combat scout).
Their com is, again, a mixture. It is the second strongest com, it has nanoregen which was originally a UEF thing, double RAS which is an Aeon thing and the tactical missile pack which again is a UEF thing and I can't think of a Cybran thing but that is enough to justify my point.
And Seraphim really annoys me for that reason. I would have preferred that it was left out as a playable faction rather than the unimaginative copy n paste job they did with making it from a mixture of other faction's abilities.