Therefore, criteriology was never about historicity.
So the form critic’s task is to separate the various strata in the Gospels. Some details belong to “the original historical tradition” and other strata belong to the author. How to separate these is the aim of form-criticism.
But why should their be a difference between the “original historical tradition” and the overlay from the author?
The form critic answers this by pointing to another assumption: that the gospels were composed by “Hellenistic Christians” who were removed from the original Palestinian Christians who were responsible for creating the earliest traditions about Jesus. The Palestinian Christians initially created oral traditions, not literary ones. It is these oral traditions that were taken by the later literary Christians and reshaped into written narratives expressing a particular theological point of view.
The form critic’s job was to break apart the units of early Jesus tradition from the theologically influenced narrative of the Gospels.
Once this was done the form critic would use these “free-standing units” to reconstruct the earlier oral tradition of the Palestinian church. […]
Form criticism was meant to discover the pre-literary oral tradition.
From the 1950s on scholars sought to discover something else: they sought to find the authentic Jesus traditions — the historical Jesus with the tools that had been designed to find the pre-Gospel tradition.
So for instance, the Criterion of Embarrassment was never meant to find out what the historical Jesus did. It was meant to separate what served the interests of “the Church” from oral traditions that (might) have gone before it. Current historical Jesus scholars have taken an extra step: assuming that “oral tradition” meant “historical Jesus”.
Over time, the “oral tradition” part is completely ignored and criteriology is assumed to uncover information about the historical Jesus full stop.