Sieges are easily the worst type of battle in Total War Warhammer 2. Siege towers and battering rams are fricking useless, there is no reason to put your units on the wall and the sieges aren't balanced, Legend is even able to beat them with one unit of ratling guns, the lord and a warp lightning cannon.
Here's how to fix them:
First of all, increase the damage a battering ram does to the gate in one blow.
Then, improve siege AI where they would actually do something with their units, especially cav and monsters, if you are outside the city. Then, towers of many races are still bad, buff some of them (skaven towers don't need to be buffed ofc)
So, yeah, what do you think?