The last flag in BL is just TDM with a focal point. Since both the attackers and the defenders spawn about the same distance it's just rush in, die and repeat and hope the timer is on your side. As a defender, you know you'll never be able to push the attackers back.
Also in Warband only a few maps would allow cavalry fight at the flag. Now we have pure chaos with cav knocking everyone about and there can be no coordinated defense.
I'd like the defenders to be able to pick their spawn points, and have the attackers just be able to gain one or two forward spawns just outside the walls to save on running.
But I feel we'll have to wait for mods for a good siege since I really doubt that devs have actually played the game.