Because basically I don't think reducing the ammo would be necessarily nerfing those classes, if there is another compensation on the table.
What ammo influences is, the time those classes can stay away from melee combat (if they are avoiding the melee cavalry well). with 3 stacks of bodkin arrows, it was 48 ammunition. A very high amount for a class that is also moving very fast if you ask me. 2 stacks of bodkins with a melee weapon would make it 32. With my suggestion, they would be having 24 and 16. It is still pretty enough for a
skirmisher class.
That is why I made this suggestion and why I think it is the best way to go. Removing the ability of horse archer classes to be the
mounted foot archer. This suggestion would make them more of a
skirmishers now, because you can't balance a class that has the speed of a horse and the shooting power of a bow/crossbow; as said by someone else that I don't remember of his name.
Think of it like this. The most classified Horse Archer build is:
STR - 15
AGI - 24
Weapon Master - 7
Horse Archery - 4
Power Draw - 5
Riding - 7
Archery - 170
However with the addition of removal of Horse Archery skill penalty to wpf. You can easily make something like this.
STR - 18
AGI - 18
Ironflesh - 2
Weapon Master - 6
Horse Archery - 3
Power Draw - 6
Riding - 6
Power Strike - 6
Archery - 150
OneHanded - 50
Jackie's 15/18 build could have been even more useful. If you want, you can stick with the old 15/24 build as well. I remember using a military hammer with 30 wpf and 0 ps with that and 5 riding. It was pretty useful. Not to mention it would be actually easier with 7 riding.
By the way updated the first post a bit (that's what feedbacks are for eh?). Made it even more in favor of horse archers, since their ammo seemed a bit low for their effectiveness. It's 2/3 for arrows and 1/2 for bolts now. Which makes 10+1 bodkins, 12+1 for tatars and 14+1 for barbed (rounded down). Weight and prices are still halved down for arrows. Bolt quivers are the same because 6+1 per quiver is more than enough for Horse crossbows to be effective since their damage output is higher and it is easier for horse crossbowman to hybridize with melee. Horse Throwers are untouched because they are not an UP class as says zlisch aka. the faithful defender of horse throwers.