I would ask how do black elves and dwarves add to the story? I don't see them adding anything.
Svartálfheim (literally the home of the black elves) is one of the nine (or ten) realms of Norse mythology. Black Elves are also called Dvergs. Who are, you guessed it,
dvergr (Old Norse)
Origin & history
From Proto-Germanic *dwergaz ("dwarf"). Cognate with Old English dweorg, Old Frisian dwerch, Old Saxon dwerg, Old High German twerg, twerc.
Pronunciation
(12th century Icelandic) IPA: /ˈdwerɣr̩/
Moria and Svartálfheim share many similarities. There is a shitload of goddesses in Norse mythology too.
We are talking about mythology, essentially bullshit in our contemporary eyes of which there are dozens of versions and variants anyway.
And the fact is mythology is way more diverse than the image we may have developed of it in our wanking teen years.