> Just better encryption that does not increase the chance of nsec leakage?

Correct. NIP-44 is not a new DM NIP (that will be another number). NIP-44 just defines a better encryption scheme that any other NIP (including a DM NIP) can use. The offered protections by NIP-44 are against the needs of that individual encryption and not against the needs of a new DM system :) 

In other words, you can definitely use NIP-44 in a way that is not private at all. The encrypted parts will be private, but all the other markers in the event can give everything away. It's like citing somebody in a NIP-04 message and adding a p-tag to that person outside the encrypted component.