As I talked about in previous posts, being made to be used in a fight was one of the main focuses I had when making this. The walls are on top of a slight slope with spikes along much of it, similar to the way the city was already set up in it's smaller version. So access to the walls with ladders and towers is still somewhat limited and the defenders have very good access to it. If catapults do destroy the walls, there are numerous choke points that the defenders can use to defend at. Also keep in mind that defenders have the ability to choose their spawn points by using their spawn flags. And defenders also have the ability to use catapults which have the ability to one hit hit other catapults, killing the crew around them.
As far as issues about size being to big causing lag, if you are referring to the number of items in the map, I checked and it is smaller than several of the current very playable MP maps that are used. The actual size of the map is exactly the same as what it was before.
I also did a few time tests to see how long it takes to get places in this map. All the times are approximate.
Back of defense area to the top of the closest wall (most defense spawns however are far closer to the walls): 24sec
Attacker spawn#0 to top of nearest wall: 24 sec
Entire width traveling on walls: 55 sec
Entire width traveling behind the walls: 40sec
Throughout the whole process I intended to keep it as a difficult objective to take, but ultimately either side should need better organization, teamwork, and skill to win a battle.
Ultimately the only way to know a map works well for sure it to do some real combat tests on it with organized factions, but I've been playing strat since before any cities were taken the first time, so I think I've made a map that should work well.
In case you're interested at looking at it in person