Nerf both acceleration and maneuver. Everything will be fine after that, people will still play cav, and will still top scoreboards, but they will require far more skill, and will be seen less frequently (as they should).
As it is now, at the beginning of every round I check out how many cavalry players my team has, if it's a healthy number, I know we will win 90% of the time, and if it's not, I know we will probably lose. It shouldn't be like that.