Originally posted by cdtm
Or more seriously, Endless Death operates on a larger scale. She's directly involved in both life and death, of individual people, and the entire DCU... Of not just one universe, but all of them. She even operated in Lucifer's multiverse, and that's outside of the Presences creation..
Death is the one who claims destiny of the endless and everything else as seen in Books of Magic v1 #4:
http://i.imgur.com/I7jFMJv.jpg
.....while Destiny himself watches all the universeS (History of the DC universe #1):
http://i.imgur.com/pzU8eWf.jpg
and as you said: she has a job to do in Lucifer's creation (which is completely separated from the normal multiverse), 2008 bio:
http://i.imgur.com/kjvSKnf.jpg?1
On panel, Death claims Elaine while she was in Lucifer's creation, in Lucifer #26:
http://i.imgur.com/THSyOEC.jpg
http://i.imgur.com/uL9VjG6.jpg
This proves that Death's influence extends beyond 1 multiverse and into others if there are any (like Lucifer's).
She is also established to be more powerful than Dream who can casually create/destroy billions of universes.
That said, i do believe Death of the endless is intended to be more powerful than Mistress Death.