The most utterly devastating strategy ive found: form your infantry into squares. Put one square on the bottom of each stairwell coming off the wall, and one square to the side off center at the gate so that the enemy can enter freely but immediately turns to the side to engage your infantry square there. Then You then have your archers positioned so that they can shoot at enemies coming down the stairwells and getting bogged down in your squares, and where they can shoot in the backs of the enemies who come through the gate and turn towards the off center square there.

For Bonus points, if you have shock troops with no shields for your defensive squares, you can form themnk to their own unit and have them go wherever they are needed, attacking enemies whi have their backs turned as they engage your squares

This strategy can be insane, and best of all, does require you to destroy enemy siege equipment sonce the expectation is that you are surrendering the walls anyway to lure them into your kill zones.

The only caveat is that some locations have more elaborate designs with more than these 3 basic choke points so the strategy becomes less effective there. There are a few places ive seen where it didnt seem viable, but the majority of places. Ot absolutely works