That is not correct. All the airlines saw a similiar decline and return of traffic. The public did not hold the 911 accidents against either airline. There are lots of reasons Delta did not furlough as long or deep as some airlines. Part of it may actually have been that they had a superior low cost feed network that allowed them to maintain mainline service. In fact Delta has and had a larger overall average aircraft size in the fleet because of their strong feed. When it looked like we were going to merge with CAL as a example I was stunned to see their overall fleet makeup. It was essentially a small narrow body airline with the average aircraft size being 60 seats smaller then Delta.
The early retirements at Delta had little effect on furloughs. They shifted the timeline of returns up to a year of so. Most of the pilots who took the early outs were in their last 2 years with Delta and would have turned 60 before the age change to 65. There was a slight time shift from the ER's but no long term benefit.
Delta may have maintained more capacity then some thought was smart during the mid 2000's because the entire management stategy at the time seemed to revolve around USAIR going out of business and being positioned to capitalize on that situation when it happened. It never came to pass and much of that management team bit the dust as a result.