I have another point: Is it really the power behind a card you are measuring of the versitality.
Take two examples:
Undead host and Magical forge
The power behind undead host is real and i've seen it ending many games. On the other hand, it's only playable in Undead decks.
Enter Magical forge: You see it in many decks because it is fitting everywhere, but it isn't the card where i would argue about the power level.
On the other hand, lets look at the statistics tool we already have. It's true that cards that are played often above all decks are rated higher, but wouldn't these cards just be again on list depending on card win rate because the community has decided by play that they are the most fitting ones?
I like your idea, but i'm not convinced what you want to accomplish. Do you want a second statistic or would you like to have a number which is the ratio of won/lost games? Later one would be something great to see at least.