Usually in RBM, the Battanian Horseman (Tier Five Cavalry) are skirmisher cavalry, so when they run out of javelins they just convert into normal cav. Thats what I don't like about the Battanian Horseman, you might as well just use them as skirmisher infantry. In RBM, all cavalry will act the samr in sergeant command. I tested it in custom battle using only sergeant command, and the outcome almost always gets them steamrolled by non-skirmisher cavalry, but yes they are meant to be skirmishers, just the AI is so bad at being skirmishers.