The thing is that this game is not balanced around reality. And from the bump damage nerf and its effects it seems to me that the devs wanted to (more or less) completely remove the bump feature from light horses. On one hand to give the (massively underused) armoured horses a purpose, on the other hand to remove the rather lame feature of having guaranteed knockdown as reward for keeping [W] pressed. The high mobility and all the advantages it brings is enough of a reward for paying horse upkeep and riding skill points. If this is the attitude of the devs, I think I have to agree.
For light lancer cavalry this means: do not touch your target, and stay away from bigger groups. You are something like a melee skirmisher, which means you have to cruise and attack on opportunity. Which means you can't dictate your encounters 100% of the time any more, like you did before with riding-stabbing target #1-ridign-stabbing target #2-riding...
I don't know what I can say about 1hd cav, because it needed to rely on bumpslashing, but as I consider bumpslashing as quite close to the border of lameness, I am not sure it's a bad thing. Perhaps from now on 1hd cav needs to be heavy. Although I would agree that 1hd WPF could increase horse bump dmg, as unlogical this might sound.