Within the context of Blizzard's shitty matchmaking algorithm and ladder system, I think the balance is already too far in favor of control. It's quite easy for players to start out fresh, gain a few ranks, then run into a wall of players with 3-4 legendaries and more epics. This change would ensure that happens quicker and more often.
Outside of that context, it's a neat idea, maybe a bit OP. Haven't gone through the math, but my instinct seems to think that these cards would cause some very lopsided trades.