People who has +3 Light xbow will rage
Just like the people who had Coursers or Arabians with 4 riding builds raged when they got changed, or when my beautiful 16-24 great maul build got nerfed etc. etc.
Changing requirements on things isn't uncommon but making light xbow unusable on horseback isn't the way to go. Upping it's strength requirement while mounted to reload or increasing reload time type of thing because light xbow on foot isn't a problem.
Also, lol @ saying they'd nerf HA because HC got nerfed. Horse Archers are fairly uncommon on NA, not sure about EU and I shrug off everything but headshots from HA's anyways in my heavier armour.
As for taking down the HC, they're all high 8-10 riding dedicated HC. They're harder to hit than normal cav because their mounts maneuver and accelerate better than your standard cavalry player. Takes a little more luck with the RNG on accuracy. I made one just for fun, 10 riding and stole a champ courser. Bloody ridiculous on that thing.
With speed bonus, they do pretty significant damage (considering it's only a light xbow) and then they just run off and reload and then come back. None of the danger of using a crossbow on foot because their reload is done while moving.
I'd say it's on the strong side of the spectrum and could use a little tweak, nothing drastic though.