I think you need to be careful what you wish for.
For all the complaining about DL's fortress hub status, think about the economic impact that DL has in the Atlanta area because they have a fortress hub that results in air traffic that is far and above what the market would support based on O&D traffic alone, or even if it were a smaller hub. DL provides tens of thousands of jobs in the Atlanta region and for every three jobs at Dl there is another job in the community that is created.
Further, assuming that a drop in DL flights would result in a one for one replacement by other carriers offering O&D service totally misses the understanding of the economics of hub airports. If DL's ATL hub were smaller there would not be a commensurate increase in O&D flights by the other carriers. Don't believe me? Consider the fact that ATL serves a core market of 6 million people yet is far and away busier than airports serving 5 - 7 times more people.