One of my fears with the upcoming 1.4 patch is that defending a keep will become much harder than it currently is. The new open RvR system is focused on taking your enemies keep. When you do, your side wins the zone. Not only have the mechanics changed, but players will have more tools to use.
Siege engines have received a nice power boost. Using the single target version, I two-shotted someone while they ran by the keep. Of course, they were not a healer and had no support. The damage increase will help, but it does not scale. Versus a single warband, the 4 default siege cannons will be dangerous. If you are facing down 4 warbands, their damage will become insignificant. On the inner keep, you only get a single siege cannon (not counting mobile ones if they are available).
The walls used to be a defenders friend. Now attackers have new ways to bypass them. Rat Ogre's can toss anyone (except other Rat Ogres) up onto the wall. Also, players using the aerial bombers can parachute down or just bomb the heck out of the defenders. If you are a smaller force, holding the walls will become extremely difficult.
Tank walls will also be more difficult to pull off, thanks to Rat Ogres. They get an AoE knockback ( Charge ) which does not use an immunity timer. It does have a 45 second cool-down though. Both sides get them, so there may be a few defensive possibilities too.
One new aspect that Defenders have going for them is that they re-spawn inside the keep. No need to worry about having to run back from the warcamp. This should let defenders be more aggressive. The downside is there is no healer inside the keep to get rid of the death debuff.
While an even match up may end up being pretty competitive, it seems an outnumbered force will not really see much benefit from the keep's defensive nature. I'm not sure what can be done to resolve this, especially when it comes to the inner keep. It is just too small. Overall I think the new system is certainly an improvement, I just hope outnumbered forces can still fight in the keep.
Mild Mild West
7 hours ago