What if the Dark Star skinline just shows how certain champs would look like if they would be one of those entities? Like, to give us some vague image how they look like. So in the canon universe AS would not be fighting against DS Ori/Kha/Thresh/Varus, as they exist as their original Version, just as Sharjo stated before, but rather against similar beings ( IMMENSE, black/purple, devouring planets,stars and galaxies). That way, even though the DS Skins aren´t canon, they serve as a tool to show us the traits that would define such "terrible entities", rather than the exact beings.