I'm no superhero, just a decent SP player who would be hopeless if I tried MP.
(I pause...)
I've won battles in RTW against vastly superior opposition.

The key is routing them, which is too easy. Outflank an enemy unit, and make them rout.
Once they start routing, you just have to look menacingly at the rest of the enemy army. "Run away!! Run away!!"
Of course this is bordering on an exploit, especially if one uses cavalry, but of course one hardly does. I can't help it if they put the general on a horse!