Jon Peterson’s year-in-review linked to this article about mana that he had contributed to.
How could the concept of mana as a generic spiritual force become invalidated and ubiquitous at the same time?
That kind of thing strikes me as utterly normal.
The first modern role playing game, D&D’s key innovation was to combine the rule systems of tabletop wargaming with the setting of fantasy fiction and the interpersonal improvisation and role-playing that had been percolating in gaming and fan communities for years.
That may be the best, most concise explanation of what D&D did that I’ve ever read. It is clear (especially if you read Jon’s book) that all the elements were in play before D&D. D&D brought them together. Which ought to be unsurprising, because that’s how these kind of things usually happen.