Weather affected the airlines fairly evenly this winter. DL has ATL and MSP, but UA has ORD, IAH and East Coast stations, and AA has DFW, CLT and ORD. Over and above IT issues affecting scheduling, it looks like DL also has a bit of a crew (particularly pilot) shortage. Many of the cancelled DL flights from hubs cite "operational" reasons, and there are spare planes there that they can use in case of a mechanical, so crew issues are most likely to blame for all those non-weather cancellations. I think DL needs to use some of its profits to hire who they are short of and return to becoming a reliable airline again.