Yeah... in other words, it turns out that the best tactic for Stronghold is to develop a captured castle belonging to another faction. :)
I just don't understand what the point is in playing as Stronghold against strong players or at least players of a similar level. In my opinion, you might not even be lucky – a neutral castle might appear without a Fortress, or there might not be one at all; there might be too few resources, etc.
What then? Should you meekly wait for the enemy army to arrive and die with a sword in your hand? :)