I hopped into battle last night, and what glorious sight met me there? Random Plains!!!! Not a roof-top in sight, nobody wasted a slot with ladders, and there were no crappy buidlings for people to scurry into and leech.
I expressed mild (pleasurable) surprise, and wondered aloud how cavalry was doing in this fight. I got mixed answers of "raping me" or "being raped". I hopped on my powerful steed, took my javelins, mace, and shield to hand, and rode into battle with my friends. What I saw shocked me!
I saw groups of infantry following their archers to their hill. I saw archers focusing on clusters of targets that sprouted arrows like a bird sprouts his winter plumage. I saw groups of polearm users setting up where they could protect their ranged from any incursion. I saw players with shields sticking together and advancing with support from their ranged and cavalry, while 2-handers and polearmers followed closely, waiting to strike the moment the enemy was close enough. I saw cavalry circling the mass of enemy fighters, distracting the enemy and harassing any foolish enough to separate from their main troop.
What I didn't see : I didn't see archers survive when they separated from their troops. I didn't see cavalry survive when they stood still long enough for ranged to draw a bead. And I didn't see cavalry charging in and steamrolling anyone. Cavalry that mixed it up in the main mass either got dehorsed, or shot from their steed with ease.
It was a great time for everyone I think (though there may have been some disgruntled peasants, they generally died well before I engaged in close combat), and showed that when a team pulls together, there isn't a single OP factor in this game. Each troop type shines in it's situation. Cavalry did their best work when they could distract/separate, then attack. Infantry did theirs when they could stick together for protection. Ranged did theirs when they were supported by their team. Even with no rooftops, ranged got huge amounts of kills, but the "Range is OP" whining stopped for that battle.
TL:DR : Even in random plains maps, cav isn't OP, it's just what you make it.