Wrong. What you had were ordinances and legal opinions that were passed down orally from teacher to pupil. These set of oral laws were only codified as the Mishnah during the 3rd century AD - well after the time of Jesus. (The
Pirkei Avot AFAIK is also only formally codified around that time.) In the three centuries following the redaction of the Mishnah, Rabbis (note that I capitalized the word: I’m referring here to the Jewish scholars of the period
after AD 70) throughout Palestine and Babylonia analyzed, debated, and discussed that work. This is what we call the
Gemarah. The Mishnah was then paired with the Gemarah along with a few other things such as
Baraitot (traditions not incorporated in the Mishnah); taken together, these elements comprise what we call the Talmud. The Babylonian Talmud - the fruit of the analysis of the Rabbis of Babylonia - was compiled at around the 6th century AD (ca. AD 500), although editing continued for some time after that. Its Palestinian counterpart and the older compilation, the Jerusalem Talmud, is older by a century.
Here’s the thing. Oftentimes the Rabbis of the Mishnah presented some things as if they are already long-standing tradition: the Mishnah claims to preserve an accurate memory of actual practices and legislations before the destruction of Jerusalem and the Temple in AD 70. Some at least have historical credibility, but the problem is that in many other cases, what you had wasn’t actual historical memory but most likely Rabbinic fantasy - or at least Rabbinic exaggeration. Between the 1st century (the time of teachers and sages) and the 3rd (the codification of the Mishnah by the Rabbis) a hundred or so years elapsed wherein much of the oral teachings were altered, adapted and recast.
Well then they may have not been written down at the time but they existed at the time which is my point, there were laws at the time, maybe oral but the fact that the law was oral doesn’t mean there was no law at all.
The Mishnah portrays the Rabbis as being charge of the Temple, that the Sanhedrin is a rabbinic operation (the Aramaic term is really from the Greek
synedrion “council;” it most likely originally simply referred to the high priest’s ad-hoc advisory councils as opposed to the formal organization envisioned by the work), and that high priests and kings obey Rabbinic instructions. In other words, what you have in the Mishnah was the Rabbis imagining how they would have run the Temple and Israel had
they been in charge. The Mishnah really describes how things “ought to have been” (as opposed to “how they were”) using shards and remnants of historical reality. As Rabbi Jacob Neusner (
The Classics of Judaism: A Textbook and Reader, p. 30) said, “the Mishnah tells us something about how things were, but everything how a small group of men wanted things to be.”