They can, any we made decks pitted against each-other each have a chance of winning. Rainbow still has an advantage of a large card pool, less of a niche to conform to, and less things that can jst out-right make it topple.
I assure you, for half the elements right now I can think of some way to take them down, for the elemnts i've played, I can think of three major things just for one that would topple it. May you list a few viable stratagies against all rainbow deck, and all rainbow possabilitys are included in that, because its a lot easier to do that for ever mono and dou deck.