I have been mulling over this "rainbow/non-rainbow" discussion. After some good thought, I feel the decks we use do not need to be as harmonious as I originally thought. Yes, I do want some rainbows, since no other team can do them, and they work, but we do not need a huge amount.
We are team "Underworld", not team "Rainbow". We are the leftovers from the other elements, but this does not mean we are every element. We can choose to use any element, this is our strength. The other teams have to stay loyal... we are rebels. We can use rainbows, monos, duos, anything under the sun. So let us use diverse and powerful decks, and not get caught up in numbers.
The trick to this line of thought will be in salvaging. No matter what (obviously), we will need to salvage useful cards. This is where our rainbow awesomeness will come into play. We can salvage cheep useful stuff from each defeated deck and build a new rainbow out of the scraps. We can transform the 'ick' cards then into quantum pillars and, we have a useful deck! No other team can do this. They are constrained to 50% their element, which really constrains how they salvage. So let us build a vault consisted of 8 awesome, diverse decks that can take on anything and let our strength in using quantum pillars be our strength in salvaging.