Down side of how M2TW is currently set up is that a Blitzer will win because of the innate advantage that an agressive style has with the current set up.

If you sack a city, wreck all of the building, and use the cash to buy merc while ignoring infrastructure you can move very fast and build up a massive army. In the short run (10-20 turns), the blitzer will generate far more cash than a turtle while having far less to spend money on besides their army. Net result, the blitzer will hit you with a far larger army.

If the map were large enough, and the innate cost to hold provinces great enough, you would get to a point where a turtle would win. As is, the game is not set up for that, so one would lose.