s3rialthrill3r: Disclaimer: I am not an experienced player and have only just started
Wait wait! I think it still is a numbers game. Consider damage and hit points. Somebody mentioned that you can't throw nine groups of pikemen at a sky drake and win. Doesn't the reason for that lie in the numbers, such as damage and hit points, and not tactical maneuvers such as flanking and ambushing? And what about experience, doesn't that all simply come down to numbers again?
The issue is that there are a lot of unit specials and spells that can completely change combat. For example, the sky drake is flying. This means that the pilemen are going to have a lot of trouble ganging up on it, which is one of the main reasons they lose despite outnumbering it -- it can engage units of pikemen one at a time. If you cast a spell on the drake to remove its flying ability, the pikemen could probably swarm it and beat it.
If the pikemen fought someone with weapon immunity or an illusionary attack, they would also tend to be screwed, because their weapons can't do much damage against weapon immunity, and illusionary attack will negate their armor. On the other hand, if they had magic weapons or true seeing (which they can get from appropriate spells) they could fight back with no problem.
Or someone could just cast confusion or sleep on them (or their enemy), which would make the whole point moot unless they had magic immunity!
The game is heavily influenced by Magic: The Gathering, and part of what it takes from that is the idea that victory often comes from using your spells and unit special abilities, rather than by just swarming the enemy. Finding a good combination of powers (or figuring out how to use your powers to hurt an otherwise-difficult enemy) is really the core of the game; hordes of pikemen are going to have a lot of trouble against air elementals or illusionary warriors if you don't plan ahead and think up ways to negate their weaknesses.