[quantum_mechani]

I think there are really two issues here:

1. People building cheap castles in every province.

I don't think this is a big issue, it is only a real option in long games, and it is only powerfull if the player can back it up with strong armies/SCs.

2. Only a few of the forts are worth the design points.

This is the real problem in my opinion. The watch tower costs no points, while remaining cheap in game (and quick to build), and providing most of the defensive power of other forts. If each of the citadels cost zero points, they would have still in most cases be inferior to the watch tower. The rest of the forts fall somewhere between, but I don't think anyone belives citadels are a good choice as they exist now.