"Good" content is in the eye of the beholder. For you, content equates with gear and gear alone. You are missing the main thrust of the expansion if you fail to realize that Campaign covers much of the content of the expansion update. As I already said Campaign is just different content. If they had just recycled Assaults they would have been criticized for doing that too.
File-size of the expansion disc is a horrible indication of raw content. You are making assertions without much logic. What actually comes on the expansion disc? The maps for the zones and a few other things. The Campaign system is not of equal size of Besieged, but more like running several simultaneous Besieged events in open areas where other content is also occurring. And if you hadn't figured this out yet, everything in this game is about the same thing - to "kill mobs." To criticize game content on those grounds is to criticize the entire game, and actually just about every MMO, hell even most video games ever created.
In the end, you may not like the content they delivered, but this does not mean there is less content. And it certainly does not mean that they will put out the next update any faster because there was "less content." The amount of development time does not change just because you do not like Campaign.