There were at least 24 known sects of Judaism which existed in the 1st century, not even counting those sects which were considered Judeo-Christian. The heightened political turbulence of the period and failure of the Hasmonean Dynasty to develop into long-awaited Messianic age meant many Jews were frustrated and looking for answers, esp. after Roman rulers crushed the independent State of Israel. Into that backdrop were many who were waiting for the end to come, AKA apocalypse, even fleeing to isolated caves to form religious sects (eg Essenes, in Qumran), a location which was used by many such types for many centuries before and after Jesus lived.
Being that's there no independent contemporary record of Jesus existing, I suspect the odds are great that there was such a person with a group of followers existed but was crushed, just like all the others; hence the story of the group could be the story of MANY similar groups where disenchanted and disinfranchised individuals would give up everything they had to follow a pied-piper (sound familiar?). Fact is, such a person MIGHT have existed, but that is irrelevant: it doesn't prove that he was the Son of God, able to perform miracles, etc. Anyone could claim ANYTHING in writing; doesn't make it true (and there are at least three Isaiahs who wrote the book; writing in someone else's name is hardly a new thing).
It seems likely some of the details found in the NT narratives sprung up much later to add details that are amalgams of legends, true events, and myths, and a literary genre was born that took off with readers, spurring on "me, too!" books (think of the recent teen Vampire-themed novels that go thru cycles).
You'd think that even something as simple as determining exactly who discovered the Dead Sea Scrolls circa 1945 would be known and easy to determine, but it's not: there's many versions of that event floating about, where all differ in the exact details. To expect to know with any more certainty of events which occurred 40X further back in the past is more fraught with peril.
Adam