I can offer the Michi-bot’s take:

A short clarification before we begin: the answers are given by a model that uses Rabbi Michael Abraham’s sources and tries to reconstruct what he would answer. Therefore, the answers do not necessarily reflect the Rabbi’s own view. In addition, the model was trained mainly on analytical and philosophical materials and less on halakhic materials. Therefore, one should not derive halakhic rulings from the bot’s answers, and when a practical Jewish law answer is needed, one should consult a halakhic decisor. The model is especially suited to intellectual-philosophical questions and to principled and meta-halakhic questions.

I would suggest separating a few layers:

What is actually “supposed” to come from the Sinai revelation

According to the Rabbi, Sinai did not come “to provide information” about what is good or bad (that can, in principle, also be known without it), but rather to establish normative obligation: to turn moral truth into a religious-halakhic duty. If so, the very fact that the text looks as though it was written by human beings is not a problem: the command and the obligation can be conveyed through human-cultural language without that undermining their normative content.

Updating probabilities, not “all or nothing”

You are describing the move correctly: first philosophical reasons for God (and for a principled expectation of revelation), and then the tradition serves as reinforcement. In such a model, the fact that the Hebrew Bible (Tanakh) looks human is not a “refutation,” but at most a slight downward update—and in practice not always even that: if divinity is revealed to human beings, it is to be expected that the message will be embodied in human language and style, and sometimes also through layers and redactions. Therefore documentary criticism is not devastating either: in a “thin” theology, multiple layers can fit quite well with the assumption of a shared foundational event at the beginning (revelation), from which the documents branched out and were edited.

Why “a religion that developed in a purely human way” is not a better explanation

There are two considerations here that the Rabbi emphasizes:
• The obligating foundation: if Sinai is merely a literary myth, there is no objective anchor for obligation. That is why there is logic in the historical insistence specifically on Sinai (more than, for example, on biographical details of the Patriarchs).
• Causal power and not only educational-narrative power: the Rabbi proposes an understanding of an “operative myth” — not just a story that educates psychologically, but a focal point of long-term causal influence. It is hard to understand how a myth in the modern narrative sense could sustain generations of practical commitment and normative solidarity; it is much more plausible that there was a real foundational event that served as an anchor.

“Human” is not a contradiction to “divine”

Even if significant parts of the whole—language, editing, interpretation, and even the development of Jewish law—are human products, that does not contradict the idea that the initial source of obligation comes from revelation. The history as the Rabbi tells it sees Sinai as the event that granted binding force, and on top of that a legitimate human-halakhic process was built. So, for example, in the relationship between “natural worship of God” as opposed to ideal laws that were added at Sinai: there is an earlier natural-religious value, and Sinai formulates and ranks it. The meaning is that a human stamp in the sources is not surprising—it is part of the way a divine command is absorbed into a human world.

Bottom line: in a probabilistic framework, once there are philosophical reasons for the existence of God and for a principled expectation of revelation, the human appearance of the sources is not a weighty argument against it; sometimes it is even expected. By contrast, the ability of the Sinai tradition to serve as a source of obligation and as a causal-historical backbone over thousands of years דווקא points toward a real foundational event, and not merely a slow human development.

Would you like me to spell out a particular point, or present additional sources / follow-up questions?

Sources actually used

“The Meaning of the Giving of the Torah (column 220)” — https://mikyab.net/posts/62809/

Those Who Are Here and Those Who Are Not — a discussion of myth, historicity, and Sinai (chapters on “operative myth”). No reliable URL found.

No Man Rules the Spirit — a discussion of biblical criticism and the documentary hypothesis in the context of “thin theology.” No reliable URL found.

“An Explanation of the Rule ‘We require that Scripture repeat it to make it indispensable’” (post; in the context of the value of natural worship of God as opposed to halakhicness after Sinai). No reliable URL found.

For a deeper and more accurate picture, it is recommended to look at the cited sources and also search the site that contains all of the Rabbi’s articles: mikyab.net
On the site you can also find how to purchase the Rabbi’s books.