I believe my reply in another thread is apropos to this discussion, so I hope it's acceptable to link it.
The question of rare freak results is probably not that helpful - obviously, they can happen and should be possible in a game. Obviously, by definition, they shouldn't happen very often.
The real issue is what should be normal, and therefore what should the player reasonably expect, and therefore what strategy will he adopt.
The fact of an 18th c. general's life was that fortresses usually could defy an enemy until a systematic siege conducted according to Vauban's scientific principles was prepared and carried out.
In effect, that meant that generals ordinarily expected not to able to take a fortress quickly. Nor could a fortress be ignored and left behind one's line of communications. Conversely, a general on the defensive could be reasonably secure either inside or behind a line of fortresses. The result was that siege warfare dominated the era.
These realities shaped 18th c. strategy and therefore the nature of 18th c. warfare. If fortresses don't function in the game they way they actually did in reality, players will conform their strategy to this different reality and the game will not resemble it's topic.
I don't think I've played enough yet to say with certainty that fortresses don't work the way they should, but I have seen some worrying indications. Fortunately though, AGE has a sterling reputation for sticking with their designs until they get them right, so I am sure all will be well.