In the scheme of all the things that DL needs to fix to come close to matching their rhetoric, this is massively low. That said, I do much prefer other carriers numbering and more than anything, their consistency. I knew most of NW's TATL flights, at least those I flew regularly, and when needed could call CS and simply tell them the specific flights I wanted. This was particularly useful when I was somewhere without computer access and needed to book/change flights.