Not sure DL’s 767s are more reliable than AA’s. Took flights recently to the EU on DL - both ends on 767s on an open jaw itinerary. There were maintenance delays on both ends, and a significant one on the outbound flight. I’m sure it doesn’t happen routinely but it’s the backbone of DL’s international wide body fleet. It will be great when both airlines retire these klunkers. At least, AA is doing it sooner.