Agree with CryptidByte, the way to nerf cavalry is to make it too expensive to lose in frontal charges, even if it does inflict a lot of casualties in the process. Frontal charges weren't the norm in this timeframe, but were done, most of them successfully but still too often unsuccessfully. When they worked, they were battle winners, but when they failed it was disastrous.
In the High Middle Ages, the heavily armored knights often lined up in the CENTER of the army, and conducted a frontal charge to open the battle. This, however, is NOT the High Middle Ages, and cavalry still don't have that kind of hitting power, although the infantry also lacks the long pikes for dealing with them.
Note that the previously discussed battle at Omdurman is described as having the horses "slowed to a walk" by the initial contact, and fight their way through with sabers and maces, NOT that they engaged at a walk. The initial impact using light lances was completely insufficient to break the infantry, and the infantry was confident enough not to break and run to avoid the impact. While 30 of the lancers were thrown from their horses, it also states that over 200 of the enemy were "overthrown". You don't do that by walking into them. If you're going to point out the 30 as proof of failure, don't ignore the 200 which point to the success of the charge. Once the lances were used, many of them would not be retrievable without dismounting to pull them from bodies, and it was standard procedure to continue combat with other weapons after the initial shock.
The point I'm trying to make is that ramming the enemy is NOT the purpose of the charge, the point is in forcing the enemy to dodge aside to avoid the impact. A wedge formation puts ALL of the threat onto a single point in the line, and if that breaks, the flanks of the wedge have the opportunity to take advantage of the chaos caused by the initial infantryman trying to push his way past or through the soldiers beside him before the collision. If that first infantryman panics, there is a high likelihood of the cavalry facing almost NO spears as the whole mass of troops tries to flee to the sides. The ones who fail to get out of the way in time are either lanced or trampled. The situation as described by the historians in that battle are what happens when the infantry actually feel confident enough to stand their ground, take the charge, and accept the inevitable casualties. Those infantry in the front ranks aren't "bumped" and lightly bruised by the charging horses, they're seriously injured or killed, whether they manage to halt the cavalry or not.
As pointed out, the cavalry will generally not charge the front of a line of spears, even though they'd probably inflict more casualties than they suffer, in part because the VALUE of the cavalry (and riders) is so much higher (especially in their own minds) than that of the infantry, and in part because they have the mobility to break off and try again at a more favorable moment, while the infantry have no option but to suffer the charge if/when it is made. The player SHOULD be able to order a frontal charge, and it SHOULD inflict serious injuries and kills, but the cost of doing so should be painfully high. A flank or rear charge should be deadly to an infantry unit not prepared to receive the charge, with little loss to the cavalry.