Too bad that this company doesn't care about 1on1. I wouldn't even expect them to balance it or to care at all, but just enable it for those who want it. 1on1 Arena with healers and tanks excluded. That's it. Enable it and live with the fact that players will flood your forums with tears, it still would be fun for a lot of us, and NO ONE is forced to participate.
I wish we had 1on1 arena and a tier list like in other games, for example this one (just a random, old tier list for Street Figher).
The numbers just show the probabilty of a class to win against another one, so a 7 means 70% chance to win, or 7 out of 10 games. I think the data is collected from tournaments and so on.