While it’s cool and fun to draw up parallels and archetypes in various myths, all myths are something of their own. Matching archetypes do not make two stories the same. I’ve read Joseph Campbell, he’s pretty much the most well-known comparative mythologist, and rightfully so. I love his work, and it has value to this study which cannot be ignored. But, I do not believe in the word “monomyth.” Tales and myths have striking similarities, but no, they are not the same story. They may even be complimentary to a model like Joseph Campbell’s, but no, they are not the same story.
The Creation stories of the Bible in the Old Testament or the Torah are myths meant for earth, and Tolkien’s Creation story is meant for Ea, his own sub-creation. The Creation story in the Ainulindale and the Valaquenta does not have two contradictory accounts. The two Creation stories in Genesis are a discussion all its own; so many theological essays comb through this, and many Christians tend to argue that the two stories are complimentary to one another. But those who read the same text are not in agreement as to the true meaning of the stories. Branches of Christianity tend to be in serious disagreement with biblical interpretations, not to mention Jewish interpretations. The argument for the validity of each interpretation sometimes takes precedence over the myth itself. The two Creation stories in Genesis are perhaps many many myths. So, this myth is just beyond me. I have not the knowledge to thoroughly address this question. But I have one, is Creation of the world the foundation for this myth, or is it what the myth “means?”
Tolkien’s myth, even if it were subject to debate, which of course someone could find something, is not a matter of actual belief. I’ve never seen anyone actually believe the Ainur or Melkor or any of the lore of The Silmarillion exists in the reality we live in. If any of y’all have encountered this, correct me, and shock and disturb me (may Eru help them). I don’t think this is a the-Force-is-real kind of thing. There is less at stake here, because (hopefully) there is no true worship. Yet, of course, this does not make this story any less of a myth. It has the same value of a myth meant for earth, for people read and tell all stories, because stories speak to them.
Of course, I have delineated something already known, for these comparisons are obvious, and in many ways can be argued to be insignificant, but I’m not writing a paper here. But, comparisons between these two are both extremely limited and extremely vast. As I discussed above, the Old Testament/Torah Creation myth(s) are the same text, only way too many myths. It is like being in a room full of butterflies, each of a different color, and trying to catch every single one at once. I see this as a limitation, at least for myself. For stories are to be read, and readers are at least just as significant as the stories themselves; they bring them to life.
Now, I can dig up all the comparisons like Ainur/Valar-are-angels-but-not-quite-and-here’s-why, or Eru-and-Yahweh-are-similar-gods-in-these-ways, or men-are-the-Children-of-God-and-elves-are-the-Children-of-Illuvatar, or,–my least favorite–how Tolkien’s own Christian beliefs seeped into his myth. But, I just frankly don’t want to.
This topic is quite broad, and one can write a dissertation on this question. It is an undertaking indeed, but I hoped I was able to provide a smidgen of insight.