Now I almost do not see any defense. People got the keep and move to the next (after small repairs). This become zerg game - same as in GW2.
From the other hand defense is very effective and small group can defend for quite a while waiting for reinforecements, but there is no reason to stay at keep and defend it, there is also no reason to buy forward camp, hire, only reason why people buy siege weapons is that there is not much to do with Alliance points.