[HJFudge]

Another thing I think you forget is that an enemy investing in any amount of raiding forces (11 is 2200 gold total, NOT cheap) is investing in a one trick poney. They might be good for raiding but really what else use do they have? Any real army will roll over them.

Second point. A fort and lab and mages all have many uses outside of stopping a raiding force bonanza. After said raiding forces are stopped or at least controlled, you can turn to more offensive uses immediately. Its a much more quality investment.