You never had a substantial amount of evidence that indicated that the Dark -type moves indicated literal darkness.
They indicate darkness a good portion of the time, even if the indication is not always direct.
You don't have enough. 2 moves out of 29 is not significant.
But it's not 2.
Nocturnal behavior isn't special among Dark types; the majority of nocturnal Pokémon aren't Dark-types in game.
So? Dark types are not very numerous, so it's not at all surprising that most nocturnal pokémon aren't dark types. On the other hand, quite a few dark type pokémon are nocturnal. That's the more relevant proportion, furthermore, the implication of a dark type being nocturnal is different than another type being nocturnal.
Most Pokémon are already "good". How far can you take that concept and apply it to Light-types.
That's a moral quality. Light as a type could be characterized as channeling "holy" energy (using "good sauce" as a means, where good sauce presents as something that appears radiant like light, akin to how dark type's "evil sauce" presents as shadowy stuff). It could also be characterized as having particular ends which are holy (not unlike dark, which has underhanded tactics, or fighting, which is righteous in intention, but distinguished on the basis that light's means are spiritual instead of based in martial arts).
How does Dark's usage of "metaphorical darkness" resemble actual darkness? Don't you even pay attention to the Pokémon moves? That is the major flaw of your argument.
Many of the moves do; hence my list. Dark, shadowy purple is often used as a motif which resembles darkness.