Angry Grimace
Two cannibals are eating a clown. One turns to the other and says "does something taste funny to you?"
I suppose I'll come out and say it, too. I don't believe balance is a good mechanic, especially not one to design a whole set around. Having to care about fiddling around with numbers just does not seem like an interesting space, especially if you get punished for using too many balance-enabling spells and equipment (you can give a 1/2 creature +2/+1 only once). I was hoping you'd discover this for yourself when you started designing commons.
I encourage you to look at your playtests and determine what you actually enjoy about the mechanic, because I can assure you, it's related to something the mechanic encourages you to do, not the whole mechanic. Perhaps you would rather have a mechanic that encourages using a lot of equipment and/or heroic or a variation of it.
The big problem with "Balance" is that it doesn't function at all due to a somewhat un-intuitive twist of the rules. It's an ability that seems like it should work, but it just doesn't work and never will because ability-adding or removing effects are applied in Layer 6 and power and toughness altering effects are applied in Layer 7. The end result is that the ability simply cannot function.
The fact that it seems like it should work is why nobody's actually mentioned it. I didn't even think about it until way after he showed us a few of those custom cards.