It seems that the tickets indicate the flight was purchased through Delta. Wouldn't it be necessary to address these claims with the carrier from whom you bought the ticket, rather than the carrier who operated the flight?
No, the claim is to the operator, not to the ticker originator. These are claims related to "irregular operations" in aviation speak, so are the responsibility of the operator. This has weird impacts sometimes, but in most cases the operator and the ticket originator are the same for most people so doesn't much matter.
