If the terrain at the base of the walls were considered difficult terrain it could model the effect of a ditch or if it took the attackker significantly longer to scale the walls they would also be more vulnerable to enemy fire.
These forts were not obsolete in ETW`s time frame, but they became increasingly more obsolete when rifles artillery appeared as rifled artillery outranged the fortifications`own guns.
However they should be perfectly possible to defeat after a siege or as a surprise assaut if the fortress is too lightly garrisoned, but to my knowledge there has never been a successful storming by line and light infantry on a prepared bastioned fortress without a successful siege in advance and without support of siege artillery.
In ETW there`s absolutely nothing to gain when you lay a siege.
Bookmarks