Am I right to be frustrated that my professor does not actually teach?
If I understand correctly, the professor has:

assigned readings
facilitated online discussions
given written assignments and quizzes, and graded them

But:

the professor does not himself participate in any activities (lectures or discussion)
the online discussion format does not lead to many useful interactions with peers
the professor gives only superficial feedback to written assignments

This does seem like poor practice. You are attending university partially to gain from the professor's expertise, rather than just reading books and discussing with peers. This is a class, not a book club. I acknowledge that there is a legitimate teaching style that involves activities, discussion, group work, and/or individual interactions rather than lecturing. But if your professor is as hands-off as you describe, I do not believe he is using this method, or at least not effectively. At a minimum, I submit that he should provide more detailed feedback (even at the cost of grading fewer assignments) and post a few comments in the discussion board to raise the level of the debate.
Despite this, I doubt there is much you can do. The professor did curate a course for you, facilitated group discussions, and is grading several pages per student per week (which may be a significant time investment). So unfortunately, I doubt that complaining to the department would lead to significant changes, at least in the short term.