the explanation of the DMs was made by jb55 and Jeffg at the nostRiga event and you are forgetting the new nip-44 encryption
NIP-44 is just a part of NIP-17; it only handles encryption and is not a complete DM spec.
yes nip-44 is an attempt to improve encryption also nip-04 is just encryption so you can use it for lists and settings in the clients and also for DM, IOT device.