Hillel the Elder and Jesus were contemporaries, according to the stories.

[Major Nikon]

90. All academics have various biases

Their credibility depends on how they control for those biases and there's numerous academics both religious and secular who have considerable credibility on the subject.

There are very few first century documents that exist today compared to the evidence we have for them. The reason is because such documents from that time were highly frangible and subject to being lost by fire, flood, theft, etc. The fact that no original documents exist isn't surprising. It would be more surprising if they did. So they were scribed and rescribed as necessary, all of which induced the possibility of modification. Historians are well aware of this and have all sorts of authenticity considerations and tests they apply. If you could throw out all evidence on the basis of a lack of original documents and copies that were subject to editing, you'd have to throw out quite a bit more like pretty much everything that references Aristotle and numerous other sages throughout history.

Just because a document dates decades or even centuries after an event, doesn't mean it's worthless. If author A publishes something that author B references, but author A's work is subsequently lost, that doesn't invalidate the writing of author B. Because so many historical documents are lost, much of what we know about history is established by such provenance.

Regardless of academic standards of evidence or bias or what you believe on the subject, the claim that there is "zero" is ridiculous. The evidence clearly exists. Whether you are moved by it or not does not mean it isn't there.