The problem I see is the steep learning curve. Assuming the average casual player is only in this for entertainment, he or she probably won't actively seek out guides in the forums or wiki like I and a lot of others did. That means their only information comes from the game itself, and the tutorials there are lacking (at least in comparison to Scaredgirl's, jmizzle's, or Xeno's).
A lot of tricks that are obvious to us may not be so for that player. There is nothing in the game itself that tells you explicitly that rainbows are a possibility -- you have to either find that in the forums/wiki (which our hypothetical newb doesn't), or find that out through experience against decks in the Arena. A lot of times the initial frustration can be too much for the player, and this more often than not weeds out the casual players and leaves only the hardcore ones who are willing to grind, look up the guides, and learn the details of deckbuilding. But then again, Elements isn't really for the casual player, so change might not be necessary. No reason to fix what's broken.