i don't think you quite get the situation. The queues on Nadd are already over 2000 and it's only going to get worse. Even if Bioware increases the server load, I highly doubt they can increase it by hat much. For the next half a year or more, you'll have to log in half a day early just to get to play. Then what will happen is, the server will get a free transfer. By now, the community will have formed and people will do a mass exodus to follow their friends. The remainder, fearing that they may be left on a dead server, will follow them. The problem will transfer to the next server, while Nadd will be deserted.
Thus when put into this perspective, 15-20 levels isn't that much, as long as it's just a guild or two - because, rest assured, getting the whole group to leave is much, much harder.
How is any of this Bioware's fault? Just as those vast communities chose to invade one server, so too could anyone else move elsewhere. Imagining that Bioware could do anything to prevent is is delusional - it would only make people cry more, because they "couldn't play with their friends". No, if anyone is to blame, it's those communities themselves, failing to grasp what their presence does to their chosen server.
As i said, the main problem wih Nadd is not that it was targeted by any particular one group, but that it was targeted by several groups at once. There's simply no reasonable way to prevent that from happening, short of locking the server down - and it's simply too late for that. Hell, I'd wager it was too late the very first day of he prelanch.