Star Wars and Marvel still evoke debates about canonicity, but at least that's a bunch of authors taking things in their own directions. Tolkien achieved that kind of argument about canon all by himself.
It's actually ripe for fanfic, and why people really shouldn't get so up in arms about whether modern expansions of Middle-earth are in conflict with "canon". He explicitly called for "other hands and minds" to expand on his work. But what he achieved all by himself is so masterful that it's understandable that some want to think of it as a pristine canon unto itself.
I think this point misses a bit of context - notably the contrast between oral and written literature. Many historical legends and folklore originated in some kind of oral context, which gives rise to a huge set of interconnected stories (and it's only later that we get some kind of "canonical" version of these stories, when someone writes down one of those oral performances). The oral performances of such stories necessitated some of the attributes you allude to. The characters and plotting are formulaic and interchangeable because that makes them easier to memorize; the details are sparse and interchangeable because that allows the bard to fill in details to fit the meter and appeal to the preferences of their audience.
> And then of course modern stories are generally single-source and totally controlled.
Tolkien was incredibly aware of this written/oral distinction, and this whole post is great evidence! Tolkien uses the way that oral storytelling functions as an in-world device to explain away a discrepancy between conflicting written versions of the same story. This ends up feeling incredibly deft because people intuitively understand the nature of oral folklore, as opposed to, say, George Lucas's endless revisions to Star Wars (which conflicts with the audience's desire for a single "canonical" version.)
If only Tolkien had lived contemporaneously with Tarn Adams, they could have collaborated and done this algorithmically.
Actually that could be a fun thing to play with. Imagine elves that live hundreds or thousands of years, but generally experience the world at the same rate as humans. They might have the same appetite for novelty and new ideas that we do; their culture might sort of “run” just as fast as ours. But when the next generation of artist comes up, their idols are still there, fully in their prime as competition.
And then of course modern stories are generally single-source and totally controlled (other than comic books and that sort of thing).
And one of the major authors who sort of bridges the gap… his method seems to have been “well I’ll just run that whole historical process in my head, with the various characters and groups recording their legends and myths!”