When I said they had decent speed I meant they're not slow as snails and are thus useable. They are indeed rather slow for cavalry which is why I wouldn't really use em as cavalry. I basicly just use em as infantry. Like
@Tokek pointed out. The only real issue with this is that you can't send a blob of 20 knights around as it just becomes unwieldy and with only 5 knights a single unit can fairly easily be wiped out with concentrated firepower.
To be honest I'd love for battalions to become dynamicly prized. A minimum sized battalion adds a very different amount of power than a full sized with several hordes does. I'm not sure how complicated i'd be but it should be viable to do.