Before you give any more lectures about how history works, let me give you a friendly heads-up.
I always appreciate these. However, history works by being in the past. Historiography and historians, though...
Historians catalogue and interpret the data, the historicity of Jesus (or any other character) is what is called an 'inference to the best explanation''
Formal languages & mathematics (and in particular logic, logical inference, statistical inference, and data analysis) is central to what I do, particularly because a lot of my work involves demonstrating to professional researchers who rely on logical inference and data analysis that their reasoning is illogical and their analyses largely baseless.
a tentative conclusion of what that particular researcher believes to be the most likely explanation.
True. That's why historical scholarship, like every academic field, doesn't amount to the sum of any and every individual with a degree who proffers some opinion. Various experts with various specialties use different assessments of evidence to make conclusions with differing levels of confidence. Some historians believe that the oral tradition behind the canonical gospels was passed on reliably by eyewitnesses. Others believe that the gospels (and non-canonical sources) are incredibly unreliable in general and all we can trust is the bare minimum. There are all kind of views in-between almost complete skepticism and religious (or religious-like) faith in how trustworthy our sources are.
This is called ABDUCTIVE REASONING
It also inaccurately describes the foundations of historical inquiry. To see why, we have only to look to the reasons why we write off as ahistorical or non-historical any account of Jesus in which he is actually the son of god who rose from the dead. Historians start using
deductive reasoning, starting from premises about the nature of reality (e.g., the "laws" of physics and similar established epistemological frameworks supplied by empiricism and the sciences that tell us people can't actually turn water into wine or rise from the dead). Without the deductive reasoning that allows us to assume that phenomena like the chemical make-up of water, the surface tension of liquids, the physiological pathology underlying blindness or paralysis, etc., weren't completely different 2,000 years ago we couldn't get anywhere.
Yes, inference, inductive reasoning, various weights placed on interpretations of various pieces of evidence, and so on, are most of what historians do. It's also what most scientists do: formal deduction is actually largely restricted to mathematics in which the discourse universe is fully defined and built upon axioms rather than our understanding of external reality. Also, the same subjective reasoning behind some historian's analysis of our evidence for Jesus is behind every historian's analysis of our evidence for Caesar.
not an actual conclusion or proof.
It clearly and trivially gives us a conclusion. As for proof- that's limited to mathematics. Even in physics, proofs are few and far between and even then are limited. The formal structure of QM allowed Bell's famous inequality proof but did not prove how it should be interpreted.
When a person mistakes a guess drawn from abductive reasoning for an actual firm conclusion as you are doing - that is a fallacy called 'affirming the consequent'.
1) You don't know what I base my conclusions on.
2) This particular fallacy is ubiquitous throughout the sciences in the form of NHST. This doesn't make it ok (far from it), but it also only matters insofar as the potential problems underlying such inferences are known. ONLY deductive reasoning is potentially fool-proof. Alas, no research lends itself to purely deductive research outside of fields like mathematics.
3) Abductive or inductive reasoning is necessarily used in all historical research, including any that determines individuals as well-documented as Einstein, Podolsky, & Rosen existed. There are no axioms from which I can infer that any historical evidence is evidence of anything without assuming an interpretative framework that is necessarily at best mostly assured by our understanding of the dynamics and physics which govern the cosmos.
If anyone imagines that the historicity of Jesus has been established evidentially, or that historians agree that the historicity of Jesus is conclusively evidenced - then they are wrong, they are commiting the fallacy of affirming the consequent.
This is trivially and obviously wrong. If I define a historian as someone who believes Jesus was a historical person, then necessarily all historians do believe Jesus was a historical person. My would be horribly flawed, but I wouldn't be committing the fallacy you state. Likewise, if I conclude that historians agree Jesus was historical based upon reading historical literature by experts, then either I can't understand what I read, my sample is too small, too many historians are liars, historians really do agree on this point, or there is another explanation that still isn't an example of the fallacy of affirming the consequent.