The issue with the OP here is not unique to him. As much as people in this forum try to deny it (and I'm a former DL flyer), it's an ATL issue.
I travel weekly to a small airport (TRI) whose two main carriers are US via CLT and DL via ATL similar to the OP.
EVERYONE (with almost zero exceptions) that I have met there has horror stories about DL and ATL. People have spent nights in ATL airport hotels, hours and hours in the airport etc.
US has a fine operation at CLT (PHL is terrible - I'm not going to attempt to pretend to defend it) and it's gotten them great loyalty in this community. Everyone has US credit cards, and US is flying at capacity.
Perhaps instead of shrugging their shoulder, blaming ATC, and telling the OP that there's nothing they could do, they could actually step back, examine the TRI-ATL-XXX operation, and see what everyone in TRI is flying US?