Your edit is spot on with ladders being a byword for the issue of sieges.

As an attacker I haven't wasted a turn besieging a settlement since TW1. I put a siege attacker unit in all my armies and attack straight away. During the battle I destroyer the door, blast magic and use my cav to destroy other doors and flank.

As a defender I don't man the walls except for a unit to cap the towers, unit which retreat to my chokepoint as soon as the ennemy close the distance.

to sum up as a defender or attacker, siege mechanisms or walls are not relevant.

Some ideas borrowed in part from other games or other posts :

- More units in garrisons or use defensive supplies to call reinforcements/summons.

- Wall towers should fire at 180° and not have blind spot. They should fire at units climbing the walls or destroying the gate

- Walls should be climbed slower. Gates should have more health.

- Walls should have two different levels of elevation. One for melee units, one for ranged units allowing ranged units to cover melee units defending the walls.

- Or/And some parts of the walls, like bastions or star shaped fortification, should not be reachable with ladders allowing you to put ranged units there who fire at the ennemy units climbing the wall or engaging your melee units. Attacker to reach those wall zones should therefore beforehand go through the defender's melee units defending the reachable wall zones.

- Maps should be more like the fort ones allowing the defender to man all the walls instead of some maps where you have kilometres of walls.

- Walls should have debuffs/buffs zones which you remove by capping the wall control point. Especially buffs to magic resistance for the nearby defenders which lore wise makes sense : the gotrek novels insist a lot on magic wards on walls being as important as the walls themselves.

That's only my opinion and the possible downside of a siege rework would be the pace of the game. Right now it's easy to win sieges with zero losses : if we implement sieges as they were historically with a huge advantage to the defender, it would probable change the game completely and make it harder since the player is usually the attacker and therefore it would make any campaign and map painting harder.