Not every long pointy stick should stop a horse. That would mean any sword can, pretty much any polearm ect. I think it's good that only the heftier weapons can stop a horse. Makes a nice change and means some people actually have to use anti cav weapons dedicated (and there are actually a lot of people who do). And don't cry realism, I think it makes sense from a balance pov. Seeing as the speed bonus works against cav when you get stabbed by a long pointy weapon. If you do, your horse it likely to go down, or at least take a serious amount of damage.