would it really take that much coding to make this change? i mean, i thought it would be simple like "if card element=mark element then upgrade card.
also, it still wouldn't balance rainbow to nerf a few cards, rainbows strength is that it can use the best cards from every element, although if we were to nerf sundial by making it last only one turn then that would give rush decks a better chance against rainbow.
another suggestion to balance the game as a whole would be to completely get rid of the quantum pillars. although if he were to do this then he would have to re-balance dissapation field. otherwise the upgrade is weaker than unupgraded, and then he would also have to test the change to it. and so on. probably take a while to do.