Did a simple test a week or so ago with the players brother during the tutorial. I gave him the best imperial armor I could find (cheat menu ofc) as well as a pureblood and the full scale cataphract armor. He also had a 1h sword (forget which one) the heavy knights shield and a cataphract lance. Set all of his perks to be as melee cavalry focused as possible and sent him off to fight the groups of 6 raiders while I watched from the sidelines. All 3 times, he managed to charge at best, 4 times before being de-horsed and taken out. He did score some kills, however, with the best being 3/6 raiders dead. Now I'm not going to get into the ridiculousness of how all that armor failed so quickly (that particular horse has been beat to death so many times already, no pun intended) but you're telling me, that a "super heavy" cavalry unit cannot take out 6 guys wearing rags and wielding wooden clubs?
The point I am trying to make with this is that, with the micro management required to keep cavalry alive and the costs of the horses to upgrade them balances out their cheap daily wage. Currently, their only real purpose is to chase off horse archers (which requires even more direct micro management on top of what is already necessary to keep them alive) is balanced by them being so cheap. Until armor gets a drastic balancing pass and heavy cavalry becomes the devastating force that it should be when used properly, they are not worth more than they currently are.