Untrue, the legacies signed the agreement to leave LUV, you can't make it look like they lost something. They could easily have stayed, but they fell for the shiny new airport syndrome and signed a contract saying they would never go back.
If it were that simple you'd have a lot more than 20 gates there and be able to do international flights. You'll live with those limits because the legacy (and the City of Ft Worth's) cases against you have merit.