On this and Monolith's point, I say this:
Mono decks are just better than Multi-colors...when there is a large enough card pool. In Elements as it is, there is a very small card pool, which makes Rainbow uber powerful while making mono decks rely way too heavily on their speed and quanta reliability, since that is their only good point.
Shard, however, is a colorless card, meaning anyone can play it. Does this also make mono-Life better than any other deck because it has access to bonds? No one would complain that point, because mono-Life has a small creature base and can't generally get the number of creatures needed out to heal enough per turn for EM.
What you are arguing is that Rainbow is too powerful because of its access to all cards. Yes, I believe this is true, but it's only true because of the relatively small pool of cards. When more cards are available and mono decks are more powerful, Rainbow will be brought down in power to their level. More card pool, but less reliability.
So basically, with things as they are, you are basically only arguing about the Shard in YOUR decks...what about mono-Light? Is Light overpowered because it has Miracle AND Shard? No. Life has Bond AND Shard AND Heal...
gotta go - no power left in battery, more later