Penalty to damage at full gallop was capped at a measly 20% (or was it 10?), and Ha takes a 2% (or 1%) off this penalty with each point. It is the accuracy that matters and HA gives back a lot of the lost accuracy. Crossbows do huge amounts of damage so that 20 or 10% penalty at full gallop did not matter to them, and it was still a one or 2 shot kill.
Right now there is no point in using a bow on horse given the weakness. A pure HC however, can get 200 WPF, 10 ride, 5 HA (and this HA is the most important) and have 2 points leftover for PS or to buff strength. You reload really fast with 200 wpf, you can outride anything you cant outfight and you can damage tin cans. If I did not have a heirloomed bow would have gone over already. If you took care of your firing arcs, you can outshoot HAs.