No offense to Dode, I have seen your stats and they are very comprehensive, but I can't agree with the idea that TD differential doesn't bias agility teams. The other commissioners in the Legion League and I have discussed it at length and gone over a lot of statistical data to try to decide on the best tie-breakers to use while keeping things as fair as possible.
Consider this graph using stats taken from the NAF, a sample size of over 140,000 games played worldwide.
Even with just a simple scatter plot, it is clear that there is a distinct correlation between match-point rating and TD differential. However there is also a clear pattern of teams with access to AG4 players having TD differentials much higher than other teams at similar ratings. Some of the most profound gaps at similar ratings are between High Elves and Khemri, and between Wood Elves and Undead.
For what it is worth, in Legion we use the average match-point rating of defeated opponents as a tie-breaker in place of TD differential, and it seems to have served pretty adequately, even helping us to resolve a potential 3-person tie at the end of our current season.