It is unfortunate how little understanding has gone into the role of strongpoints and castles. OP is only partically correct. A strongpoint is designed to fulfill a tactical purpose, whether as a Vietnam-era firebase or the hastily-thrown-up-fort of an Alemani warlord. They are designed to "resist" an initial attack or threat, to "delay" an enemy while troops are rushed to the area. The forts built along Hadrian's wall by the Romans are yet other examples of these purely tactical structures. The term "castle" must be viewed very differently. By the medieval period (particularly in a period of nation-building), the role of a castles had evolved into that of a strategic and logistic center, not only acting a defensive salient, but also providing an administrative center and a permanent living place for a resident lord and his retinue, with all the necessities of home. This happened fairly early on, during a period of nation-building. By 1284, advanced, concentric castles frequently had towns built around them, established contemporaneously, for strategic and logistic rather than tactical reasons. As in the Holy Land, castles constructed in Europe (and particularly as seen in Edwards Welsh campaign) were designed to become centers of commerce and military might for a large surrounding area. The development of these castles did not happen by accident, nor was a single stone placed without the realization of the impact a castle and its town would have on the surrounding region in the future. Medieval castles were not designed to delay an enemy, they were designed to completely stymie one. They were intended to provide the logistical base for a permanent military force while the fortified town growing up around them completed the conquest of a region more effectively than any military force could. It was a feudal world, and would remain a largely rural one for hundreds of years to come.
The mention of cities as a center for civil matters is a complete misunderstanding of the period involved. Cities derive importance from the rise of the middle classes, and while that was certainly occuring in the 1200s, it had a long way to go. The English Magna Carta (which provides protections which eventually would apply to a growing middle class) was forced down the throat of an unpopular king by revolting barons, not peasants. All the civil functions that were executed by a town or city during the period, its offices and officers such as mayors, judges, courts, public works, policing, etc., all derived their power from appointment by, and approval of, the power of the lord of the castle. The truth of the matter is that cities growing up in the medieval period would never reach their full potential as centers of commerce, civilization, and importance until well after the castles and walls which protected them in their infancy were more of a hindrance than a necessity.
Failure to recognize this concept has led to a devaluation of the castle in the game. There are conceptual misunderstandings regarding strongpoints and castles which should have been remedied prior to implementation. There is a saying in the military "amateurs talk about tactics; professionals talk about logistics." IMO, Modders who have implemented the ability for the player to place their own "fortifications" and have made new industry possible in castles understand this. Judging from everything I have read about this extended development process (6 years now?), the developers STILL do not. And that's too bad.