Honestly, I think "balance" is really a shorthand for saying "win rates". It's how I use it. It's basically how wizard's has used it in their most recent B&R reports.
Number of times used in the Temur Energy bannings:
Win percentage: 14
Win rate: 0
Number of times used in the Aetherworks Marvel ban:
Win percentage: 3
Win rate: 3
I think what you are seeing is a refinement of the terminology used as Wotc has moved to more data analysis and away from top 8 results. "Balance" was used as a subjective measure of a decks win rate, often derived from top 8 results, which is what they relied on before.
So for me, the interesting thing will be to see how closely your statistical analysis of the challenges matches the data we would have from champs (if the data can be compared).