It's not butt ladders that are the main issue, there are 4 other, more pressing problems.
1. The entire design of the game funnels you towards a ranged-heavy meta even in WH3. It's less of an issue than in WH2, but it's still there. Sieges almost necessitate using as many ranged units as possible, both as defender and attacker, especially because they can curve their arrows and hit targets behind walls (ridiculous). This makes sieges repetitive and easy as the attacker. Overpowered LLs and monstrous units are the cherry on top.
2. Walls are a hindrance for the defender. This is where the butt ladders contribute. Archers aren't safe on the walls because anything can climb them and stop them from shooting, but melee can't stay there because CA can't code fighting on walls to save their lives and there's too much ground to cover, which splits your forces, so it's better to camp in the middle of the city with all your forces than doing anything else if you are defending.
3. Siege maps are too big. Very rarely will you play a 40v40 siege battle and even then it's too big. This also makes it possible for stealth units to cap the objective without anyone being able to do anything about it. 80% of the map goes unused and it takes forever to traverse the other 20%, which slows down the already labored sieges to a glacial crawl.
4. There are just too many of them. Since there is a major settlement in every province, you either fight a siege battle every turn or every 2 turns, which takes the other 3 issues to the forefront.
Also, the AI is still shit and there's no way around it, even if they find a way to fix all of these. Oh, and the tower defense thing, but you should disable it if you haven't already.