You need to be more specific with your complaints. People like to throw around "unbalanced" and "poorly designed" with no specifics of what they are speaking about. As for the map rotation, 99% of the maps are cav friendly. I can only think of 3 maps that cav is useless. The cavern map, the castle in the sky map, and the arabian town where one team spawns outside, while the other team spawns inside and above them. Its the one with the clothes lines people like to cross. Every other "town" map has plenty of cav. If you want nothing but football fields, so you can ride at full gallop, wind in your hair as you run over infantry all day, thats an easy map to make. You should learn mapping because no one else wants that map.
Also, lag is not a term related to maps. Thats your internet connection. You want to pay attention to your framerates. When you first launch the game, before you click Play Mount and Blade, click Configure, go to Video tab, and check the box next to Show Framerate. Then when you get into the game, you can see your framerate in the top left corner.