I'd say that before Covid, DL was considered by many to be a step above the other big domestic carriers, and even their international D1 service was better. Te thing where DL really used to shine back then was operationally - pretty much rock solid reliable that you are going to get to your destination on time or with minor delay even during irrops.

Since covid, that has all changed for the worse, especially the international D1 service and operational reliability/recovery... the two things that mean the most from my point of view. DL is just a mess when it comes to irrops now.