Fine. Rainbow is fine as is. Rainbow is one of the most powerful false gods out there, and with good reason to be feared. Not only does he pack a monstrous army of 8 graboids, 8 werewolves, and 8 forest spectres, but he also carries an INSANE amount of control. 8 explosions, 6 steals, 6 congeals, 4 eagle's eyes, 6 gravity forces, and 4 thunderbolts. Combine that with 10 hourglasses, and you get an insane combo that focuses on pulling out powerful cards out quickly and effectively. Rainbow even carries along 4 improved miracles, for healing. In your post, the two cards you mentioned as "counters" aren't really counters at all, but merely things you can do delay your nearly inevitable death. Black holes seem to be a solution, but unless you have a nymph, and reusable black holes, his 48 quantum towers will probably pump out more quanta than you can drain. Rainbow could probably replace his gravity forces with perhaps better gravity cards like momentum, or elite chargers though. Overall, Rainbow is fine as he is, a hard False God.
(you should mention the true counters to rainbow are rol/hope and antimatter).