The main reason we've taken such vengeance to them is the almost canonical anachronism of so many mods and so many games featuring knights fighting on foot. Granted, no armies were really fielding Romanesque legions at this point (Which would be boring if everyone was spearmen - In reality a lot of those spears probably carried swords), yet the notion of having your
knights fighting on foot seems beyond a leap of creativity.
The sad thing being they
did fight on foot, some such as the Normans and Germans doing it frequently (The latter preferring it earlier on according to the Romans I believe). But the system in MTWII doesn't cater to that. Of course you all know that, I'm an evil lobbyist for the "Keep knights on horseback" lobby.
Ideas such as yours Fenix or Crucifix are certainly options we might pursue, though the current setup seems favorable for now. There's other various ones that haven't been discussed but might be later which we could pursue too, such as all dismounted troops being the size of their mounted equivalent, so that factions who have dedicated foot infantry (Romans, Oman, Ghazni, early Armenia) would hold something over those who have dismounted infantry (Jerusalem, Ayyubids, Georgia). But that would hinge on having the quality of such dismounted troops also rise, so that numbers don't solve anything.
The role that we, or at least I, would like dismounted knights to fill is like non phalanx infantry back in Successor Times. On the flanks or in the rear.