There are 4 random plains to balance out the 4 city maps - city maps favour infantry, random plains favour cav, it's only fair for them to be in equal numbers. Also I'd count ruins and field by the river as open plain maps, so there would be 12 plain maps, but compared to random plains they allow everyone to have fun, not just cav.
I think the native village maps are the best compromise since they are generally good for all classes. They offer some cover for infantry so cav doesn't dominate while still being open enough to allow cav to be perfectly viable. Melee have the tight alleys and closed areas, ranged have roofs but firing zones aren't too good and with the reworked maps, both teams reaching the village at the same time rather then 1 camping while the other charges keeps it generally balanced.
Field by the river, everyone camps the ruins
Ruins, there's also enough houses ect for loads of people to hide in. Not to mention that tower and crap loads of other obstacles. They are not open plains by any standards. Open plains have no buildings, and very few trees, very few hills and that's about it. They are OPEN. Steppe maps are probably a closer example.
Problem is the village maps are often fairly enclosed and allow teams to camp on roofs ect (which almost all teams on the village maps do) and have tons of massive hills/cliffs surrounding the villages. Therefore I don't think they are a fair compromise because they still favour inf strongly. Only the desert ones are probably a bit fairer because they tend to be flat all round.
