From what I have been told the average pilot with no major internal lor's will need about 5000-7000 ttl and at least 1000 PIC turbine. If you have a few internal recs then all of that is out the window. They made the mins low so they could get young friends and family in first.
I think you might be right about the competitive mins being about 5,000-7,000 ttl with plenty of PIC. The average DAL new hire in 2001 had about 5,500 hrs ttl.
As far as why the mins are below that, you can only guess, but I suspect that DAL also wants to leave the door open for ANG and active military fighter pilots who often aren't high time, but adjust well to DAL's training program and have the leadership skills, judgement and situational awareness DAL is also looking for.
Will