I never play or liked horseranged but at the current state of balance, I think even if you lifted the damage cap completely, they still would be far from OP.
Footranged can take out their horses so fast, they cant just ride around close to enemy inf and pepper them from 5 meters without putting themselves in great danger. Also with the high lvl we have today, even 10 PD isnt the damage monster that it used to be, much less HA with significantly less firepower ( not sure though how speedbonus works for horseranged right now ). And then we have flags, so endlessly delaying rounds isnt possible for horseranged either.
If you really want to make sure that horseranged cant delay at round end, make the flags spawn with a circle of deplayed siegeshields around it or some other prop that provides cover.
Lastly, inf player, wtf, do not chase horseranged when you are on foot like dogs chasing cars. First *spoiler* you wont catch them and second, you are just blocking all the ranged in your team that could shoot down their horses.