Then it would just become like any other game when you get farmed by the higher ranked players, and the new players leave because they never get a chance to even play the game.
Just because something happened in real medieval times, doesnt mean its good for gameplay. If every game would go for "life is not fair, so shouldnt games be either", then no game would be balanced. Thats why we balance RTS's, to make the game fair and let the skill decide who wins.
If a RTS like starcraft didnt care if the game was fair, they'd never change it or balance the units.
But a small part of me agree with you. Sometimes its fun to play as the underdog and actually be able to be victorious. And sometimes its fun to just charge someone with a vastly bigger army and slaughter everything.
I'm not quite sure how the system works, but maybe we could opt in for something like "I agree to a 20-40-60% army strength difference" or something like that. But again, I dont really know how the system work so.