Dark-types encompass cheating, dirty tricks, and malice. You can restrict Dark to those things.
No. In fact, dark type's special and status moves reference actual darkness. And even if this were not the case, other types can incorporate complex themes in their meaning. Your criticism that the light type is too vague is pretty much baseless.
There are only two moves that are explicitly like that: Dark Void and Night Daze.
So? Even if it were only a single move, or a single ability, or a single dark type pokémon with a theme tying it to darkness, it would be sufficient to demonstrate my point.
Dark Pulse is described as a horrible aura imbued with dark thoughts, so it is an example of malice.
It seems clear that it incorporates both things.