FWIW, I'm having a hard time with sieges too. I've about given up on ladders and siege towers, because anything I send up takes major losses, even when matched against very weak defenders. I think it's largely due to being shot up by the wall tower ballistas, and the way you can't turn them "off" by running through the tower and capturing it like we could in RTW. Instead, you have to drive ALL defenders away from ALL nearby towers, which takes a long time, and exposes your army to constant fire until you can break away from the walls and get deeper into the city.

So, I've been focusing more on breaking gates, making breaches in the walls, or having spies open the gates, and then doing the zerg ground rush (as Katank described it). If possible I do that at more than one place, to split up the defenders and get through the gates faster. Doing it in several places also allows the use of cavalry, because often there will be at least one undefended gate where I can rush in a few cav units. They do have trouble maneuvering and charging in city streets, but they're good for hitting the back of defenders at the other gates, who are engaged with my main infantry forces. Cav are also good (once they're inside the walls) for luring enemy off the walls and deeper int the city, where you can engage away from the fire of the blasted wall towers.

Also, I agree the auto-resolve is wacky. The end-result of taking the objective or losing is consistent with a manual battle. I always win if I go in with a slight advantage like 7:5 ratio and evenly-matched or superior units. But the losses for my army (and the enemy army) are way, way off. I always lose many more men in a manual battle, and end up with just a handful of survivors. With auto-resolve I still have most of my army left. I think the difference may be that the auto-resolve just matches up the attacking vs. defending army units, and doesn't factor in the effect of the wall tower ballistas? I'm not sure, but that seems the only reason why my forces would be so depleted... unless I just really suck as a field commander.

Unfortunately that makes it very attractive to just auto-resolve sieges, which I'd rather not do. I think either the fire rate of the wall tower ballistas needs to be reduced, or else a return of the ability to control towers by running through them would help.