As bad player just pointed out, ranged in general doesn't take down armored horses, on their own, they are meant to be tanks, so that's sort of irrelevant. I already responded to your "crossbows can hide behind trees" remark. An archer's superior reload mobility totally negates what little cover a crossbower has on open field maps. Also, one thin little tree to hide behind puts an xbower at a serious disadvantage when it comes to trying to fight off an archer with a longbow. And my Issue with it "narrowing down slowly" is that it would essentially be giving all crossbowmen the issue with fire delay that the arbalest gives. What is the point? Especially when we have in most cases at least a 1-2 second reload time on our xbows after we shoot? Unless you wanted to talk about increasing xbow damage or range going along with this longer reticule narrowdown it would be a huge kick it in the pants to xbowers. Also, I hope you enjoy losing all of your money gradually if you want to 0 wpf most xbows as you wont be getting any kind of consistent reward for having that mini horse on your back other than the occasional range kill.
I did suggest a increase in missile speed in the OP. As for damage, I was getting one-shotted in a kuyak last night, I don't really think that damage is much of an issue. As I said, I would only carry around a crossbow with 0 WPF if I was rich, I'm not saying it's a thing for everyone. Your logic about archers versus crossbowers would make since in a ranged duel type of situation, not a real battle, where the crossbowman would not always be the target. I've reloaded in an open field several times in an actual battle, all you have to do is make sure nobody is gunning for you. I've also been in the "ranged duel" situation, and yes, there you're right, archers would kill me, supplying that I couldn't get to them, for any reason. I'm not really saying that ranged should be able to take down armored horses, If I had my way, arrows and most bolts would glance against plate armor.