Disclaimer: The following material is based solely on my speculations and perceptions.
What I percieve while playing battle mode:
- Most archers don't use priority targetting (instead of going for dangerous melee 2 handers or polearmers they rather shoot peasants/archers/other ranged classes presumably because they can't hurt the heavy armoured melee classes enough to make a difference.)
=> The heavy armoured non-shielder players can roam around unsuppressed early game, enough to close distance to the enemy infantry and start swinging. Since these players are the most effective vs infantry they will mostly come out on top in the main fight. I only mention the main fight here because it is often all that decides the outcome of the battle.
I think this is also why 2h is often portrayed as an OP class, simply because they don't/can't get suppressed good enough by their natural counter: the archer.
I know this is a controversial topic but I'm just trying to contribute, and of course I ask for your thoughts on the subject.
Note: there are always exceptional players like some archers that can completely annihilate armies but this post is about average players.