It does less damage and has less speed then one handed weapons (because all twohanded weapons suffer from penalty on horseback). The reach is only 1 cm longer for longsword then it is for 1h swords, except the mil. scythe which can't stab and has an even higher penalty on horseback.
To add insult to injury, if you use it with a shield - which is quite useful on a horseman, you end up having to have split proficiencies or lose a lot of damage, since it uses 1h wpf when used from horseback.
In short, you have no idea what you're talking about.
Bump damage is lower, unless you are a peasant, or use peasant-type gear it does not do serious damage.