The literal meaning of the Greek word αποκαλυψις (apocalypsis), is to uncover (like uncovering the head). It is not used in the literal sense in NT writings, but in the sense of making fully known, revelation, disclosure. (According to BDAG - Greek-English Lexicon of the New Testament)
It is true that it also is a genre, and the Revelation of John is not the only apocalypse. There are other apocalypses, of Biblical ones perhaps the one in the Book of Daniel is most known (from Dan 7 and out the book). Putting them beside the Revelation of John shows they have many things in common, the imagery is perhaps the most striking thing.
But though apocalyptic literature do have evil rulers or beasts taking over (for a time) the world, I am not sure they can be said to be dark lords in the way Morgoth or Sauron are, or in the conception of "the dark lord" in modern fiction. As has been said above, the beasts in the apocalypses are dream-images, while Morogth and Sauron have a very different secondary reality. The same goes for dark lords in other modern stories.
I would also disagree that the Greek text of the Lords Prayer irrefutably means "the evil one". The Greek reads τοῦ πονηροῦ (tou ponerou), which is the adjective πονηρος (poneros) pertaining to being evil, wicked, base, worthless. It also have other meanings, which all pertains to a lack or worthlessness in the physical sense - of being of poor quality or being ill/unhealthy, but here the first meaning is more relevant. The adjective is used with the article, in English "the evil". The article is used in many ways in Greek, and not all of them the same as in English, so it is a matter of interpretation what the article here means. Probably it means that the adjective is used as a substantive, which can give the translation "the evil one", but that will also depend on the gender of the article. It is not clear if the article is masculine or neuter here, because it is in genitive. In genitive the masculine and neuter have the same form. If the article is to be taken as neuter, then the translation would be "that which is evil".
The context does not help us all that much, so tradition and interpretation is what is left to guide us. The genitive comes from the preposition (απο apo), so it is not the possessive genitive, but rather the ablative genitive (here expressing separation). Some scholars favour one, some the other interpretation. The Greek text is simply ambigous on this point.
But I am not convinced that Utgadsloki in the Norse myths can be seen as a dark lord in the same way either. He don't lead armies: he has a household with household men much like a Norse chieftain or jarl, or a king (there was not that much difference between them at that time). He is not all that different from Thrym when it comes to position and power among the jotuns. It is Surt who is the most prominent opponent during Rangarokk (or at least the one named to burn the world, there is no one main opponent really).
The Vedic stories I don't know well enough to say for certain, but the concept of a dark lord as we can see in Tolkien and later fiction, seems to me a modern invention. In Tolkien it feels more like a blending - Morgoth (and to some degree Sauron) has more in common with the Lucifer of later Christian tradition (no mention of him in the Bible) than with the adversaries of Greco-Roman or Norse myths, yet not wholly unlike them.
I am inclined to think that the "dark lord" concept in modern fiction comes from Tolkien's invention in Sauron and Morgoth. The concept has deep resonances in the idea of good vs evil or light vs dark (cosmos vs chaos etc), and in gods battling monsters, or God vs Devil, but as in much of Tolkien, not a clear line from one to the oner, or a single equivalent.
I see Tolkien as the most likely direct source of the concept of a dark lord in modern fiction, but that the underlying concept of good vs evil/ God vs Devil in Western cultures made that idea resonate and gain the popularity it has.