@ Soteria
I generally agree with you but I can think of an instance where a smaller force beseiged a larger force. I'm thinking of the early stages of the Seige of Alesia. Also, if we looked, I'm sure we'd find some in the Mongol conquests. Generally when the defending force feels its troops are inferior, albeit more numerous, than the attacker, it withdraws.
Hard to say in the case of the Mongols, though you may be right. Even in well-documented battles like Cannae, historians' numbers for army sizes and casualties wildly disagree. Anyway, wouldn't that be the exception that proves the rule? It's true that sometimes a numerically larger force is inferior in combat strength, so it would perhaps be more accurate to say "superior" and "inferior."
I think it's a bit of a tough sell to say that the darkspawn are superior to humans in even numbers, though. Especially if you compare darkspawn to the human troops you fight toward the end of the game (no spoilers, eh), I'd say the human soldiers are more dangerous. Ogres, shrieks, and emissaries are dangerous, yes, but we saw 1 ogre, 0 shrieks, and 0 emissaries at Ostagar, that I remember. They probably had a few that we didn't see, but Cailan's forces had mages of their own.