I'd give my best estimation at 55 percent, for the figure of the amount of teammates that can not, in any way, combat cavalry. There are TONS of players that will never once view the forums, use a build other than their pro-status 22-16 build that features 2 points in throwing and 2 points in riding, or willingly give their full attention to the game. They spawn, press W until they feel that they are in combat, and then they fight. Problem is, they'll often get couched or otherwise killed by cav, and say "Wow that fucking cav is so fucking gay" to themselves, never considering that they could back up against a wall, stay with a polearm friend, etc etc etc. There's no way to fix this except for educating those new players that choose to accept it.
Basically, I do think there should never be more than a 30 percent disparity between the number of cavalry or ranged on either team. These classes are in no way overpowered on their own, but when one team has 200 percent of the other team's cavalry, things are going to get really stupid really fast.