Windurst has been the dominant force on the server since the PS2 release for some reason or another. However before that Sandy was.
Bastok has always been one of the lesser powers.
As for why Windy is so low, I'm guessing that people from the other nations started doing EF's or Windys people are droping the ball on them. Either way, I'm not going to complain, Bastok in first put more cp items up for sale that don't get sold as much and Sandy in first gets me more cp items to buy ^_^