Whilst it is true that Jesus and his group weren't the only Jewish Messianic splinter group, all the others were politico-military in nature
Firstly, how do you know that, secondly, so what?
However, we also know that the disciples began their public preaching within a month or so of the resurrection - in the centre of Jerusalem and at the height of a Jewish religious festival, with a reported 3000 conversions on that first day of preaching.
The only source for this is Acts which is a late unreliable document.
Furthermore in spite of this alleged huge conversion, other sources remain silent. Either nobody else noticed it going on or later Christians suppressed their accounts.
This wasn't some minor sect which the authorities ignored
And yet the lack of any documents from these authorities leads us to the probable conclusion that it was a minor sect that the authorities ignored.
because we are also told that they started to persecute the groups thgat were orming - hence Saul's trip to Damascus, during which he was converted.
Where's the evidence that Saul was anything more than a leader of a lynch mob?
Yet, if it was the Jews who produced the body, it would have been the Jews who preserved the information, as they have doe with huge amounts of other documentation.
And Jewish sources remain silent on the subject of Jesus. Why do you think this means anything other than they had the perception that there was nothing to care about?
Furthermore, whilst "For a long period in European history, Christians were the sole custodians of the preservation of written documents" this didn't even begin to be the case until the 5th or 6th century AD, if not later
But it did happen.
where is the reference in the older documentation that exists, to the effect that the Jews had produced this evidence - or are you saying that the later Christians had gone though every document and scrubbed this reference? If so, do you have any evidence to this effect?
So you dig yourself an even deeper hole. It seems more and more likely that the "authorities" never wrote anything about Jesus which simply destroys your claim that Christianity had a huge impact int the 30's and 40's.
In point of fact, there are gaps in several historical documents - not necessarily Jewish - covering the period that includes Jesus' alleged resurrection. These seem a little suspicious.
The proiblem with this argument is that this is exactly what the Jewish authorities would have been trying to combat. They wouldn't have wanted a story that the God that they worshipped had come to earth in the form of a human being
You do realise that this was not an uncommon meme in the Greco-Roman World of which Palestine was part. It's absurd to think they cared about yet another minor cult with yet another resurrection myth.