A couple thoughts to start. I'd say that under "Versatility," all of the "attempts to" should be changed to "can." Lots of low-tier classes attempt to fill multiple roles, and fail; high-tier classes might only have been trying to fill one role and end up doing everything.

One weakness of the original tier definitions is that it's kind of hard to take into account variation in power throughout the progression. I'm thinking something like Healer or Truenamer, that are mostly junk until they get Gate; or something that starts out really strong like Crusader but then fizzles a bit in comparison to other classes. People's experience with the class (both as DM and as player) can vary widely depending on whether they're playing a low-level campaign or a high-level campaign; and trying to calibrate expectations is one of the main points of having the tier list to begin with. A "Consistency" variable (or something like it) could help capture this.