The change is interesting and a step in the right direction. Large powerful kingdoms definitely became almost untouchable by the average player previously. The one thing I would like to point out though is that as others have said before, this new system tends to punish kings with less active players much more in the early game. Since they must be more diplomatic, they also have fewer raiding options as every surrounding kingdom is a potential ally or foe in the future and kings do not want to risk those future relations. What tends to happen is that dukes now grow more quickly than the kings themselves at times, leaving an odd dilemna for the kingdoms.