I'm not clear about
your meaning here, as "never" and "ruthlessly exploit" refer to the same device; that is, Forster was criticizing its use by Dickens.
Frye was talking specifically on the question of what makes something funny, in this case the use of unincremental repetition to provoke laughter. I recall how, at age 5, I'd run home to listen to Fibber McGee and Molly, waiting in anticipation for the moment when Fibber would open his closet door.
Tolkien uses this technique to a certain extent, in, for instance the
Gaffer, and the invocation of "the Rules" at the end of the story.
But in a larger sense, he could be said to have used "popular formulas" in writing in romance mode, with all the tropes associated with it. At the time he was writing, it was seen as an outworn, antiquated, and juvenile form, suitable, as he noted in
On Fairy-stories, only for the nursery. That he was able to revive and invigorate it was an accomplishment the groundbreaking nature of which we tend not to recognize, given the flood of fantasy that followed.