Saying nothing is binding but the Torah is like saying, nothing the Church says is binding but the Bible. People tend to listen to authority, and I don't think rabbis make frivolous statements. Halacha is derived from the Thorah, and many a rabbi will tell you that these pronouncements are in agreement with it. You can take up your issues of expertise to the source, which I included.
Yes. A Rabbi's interpretation of "Halacha" is derived from the Torah. Brilliant.
What you mean are "selected" rabbinic interpretations. Selected by you of course. They're all public knowledge. Because you discovered a portion of Mishnah doesn't mean they're trying to hide anything. You might wanna try letting a Jew actually define what a Jew is. Afterall, you get to define what an Orthodox is.