Not sure how likely CA is to read this, but I'm hoping it will at least get a glance here.

How to fix siege battles in ten steps: Create tactical flexibility(choices) and advantages for defenders to assist in the low rank and unbuffed garrison to have a fighting chance. Give players as much options as possible to create interesting gameplay.

 Step 1: Remove pocket ladders from the game. They are easily the most detrimental mechanic to siege battles causing the wall to be a useless defense. Bring back the pushable ladders from games like Medieval 2. This will allow the limited quantity of melee troops for the defenders to be placed in the right spot to fend off or at least stall the enemy advance while allowing the rest of the wall to be manned by missile troops to fire on the attackers below.

 Step 2: Remove the scaffolding system on the back of the walls and just revert to how walls are in most other total wars. Its important to create a chokepoint for units leaving the walls so that another line of defense can be created increasing tactical flexibility. Players can then setup killboxes or clean cavalry charges against units leaving the walls. This can either be done by using the stair style system from attila or by bringing the towers back into the wall so units can pass through them like elevators (Medieval 2 style).

 Step 3: Remove the docking system on the wall and work on the pathfinding to allow units to be positioned however the player chooses. For example, placing two units facing forward or backwards or even just having a unit sideways, again creating tactical flexibility. A player can have a melee unit facing sideways to prevent a compromised section of the wall from overrunning the rest of the wall and buying time for other units to keep firing projectiles for example. Or maybe protect the exit points from the wall so that units inside the city can fire at the attackers on the wall. Give the player the choice of how they want to defend.

 Step 4: Add a capture point to the top of the gatehouse. When a unit has control of the capture point it will drop rocks (or whatever wonky fantasy thing that faction would use similar to the bombs the current thunder barge drops) on units passing through the gate below. This is really important, it creates a strong incentive for the player to hold or capture the wall to take control of this mechanic and makes holding the chokepoint at a gate even more valuable. This will also incentivize the use of battering rams to prevent massive damage in the process of destroying the gate (battering rams should always have enough health to survive them bombardment giving them more value). This creates tactical flexibility, I'm starting to sound like a broken record.

 Step 5: Remove the deployables system, it was an interesting innovation but it didn't work. The AI has far too many issues with barricades and the towers are super annoying. Leave the capture points around the city to provide a leadership bonus to the defenders when held. As sections of the city are taken the people living there would be robbed, killed, or likely worst in this setting so the defenders would lose heart and the will to fight watching parts of the city fall. However, until the points are taken the garrison will have a leadership buff to help even the odds against the likely larger quantity and quality of the attacking force.

 Step 6: When defending units route they will fall back to the victory point, if they route again then they shatter. This creates a very natural last stand mechanic where the player or AI can setup one last ditch effort to defend the city or at the very least cause the fighting to progress through the streets as the battle continues adding tactical flexibility.

 Step 7: Allow defensive units to deploy just outside the wall, so that skirmisher units and cavalry can be better taken advantage of, or maybe just using chaff infantry to hold the advance to buy time for archers like the battle of troy. Again this just adds to tactical flexibility.

 Step 8: When two wall sections are destroyed next to each other they should collapse into one big section instead many tiny ones. This allows attackers greater tactical flexibility when trying to maneuver into the city. 

 Step 9: Fix the line of sight issues around cities for gun style units. Currently entire battles can be lost simply due to a handgunner unit just refusing to shoot even with clear line of sight. Particularly in areas around the map with the crenellations. This issue takes away tactical flexibility for the way these line of sight style missile units can be used. (Recent updates have addressed this somewhat)

 Step 10: Lean into the fantasy, this is warhammer lets see some crazy stuff. Here are some examples but not an exhaustive list.

 - Allow ethereal units to move through walls.

 - Allow spiders or other similar units to climb walls. Just imagine arachnorak spiders climbing up the walls then just plowing through ranks of infantry as they go flying.

 - Allow Monstrous infantry onto walls via siege towers, I can't think of anything more terrifying then rampaging minotaur or ogres slamming units off the walls.

 - Allow defensive factions like Dwarves/Empire/Etc. to have artillery emplacements either high up behind the walls or on the walls themselves where they can place artillery units. Even if the cannons can't get down I would happily place them there to fire away.

 - Let Tomb scorpions burrow under a wall and pop out of the ground on the other side.

 - Let us recruit foot knights for brettonia... just do it.

 - Skaven weapon teams should absolutely be allowed on walls.

This is really terrifying for me to post, so I'm hoping this provides some value in making this great game even better. :)

Well I agree with absolutely everything you have stated.

 but while CA keep saying they are interested in player input, they don’t seem to want any with regard to sieges and seem locked into their own emotional attachment to game designs that just don’t work.

Here is hoping that at some point in the future they let go of their sunk cost fallacy bias and allow for your listed improvements.

That would be a bummer if CA keeps ignoring the fans, this game has so much potential. I just want to see it realized!

I completely agree. There is so much time and effort already put into the game why not listen to some of the constructive feedback and see if any of it sticks.