By contrast you have a singular account, with evidence of subsequent tampering, ...
Evidence please.
O's "singular account" is incorrect. There is independent stuff about Jesus in Matthew, Mark, Luke and John (and some dependent stuff) as well as Paul. There is also Suetonius (possibly), Josephus, Tacitus and so on from outside Christianity.
Josephus and Tacitus don't talk about Jesus, they talk about a cult of followers of Jesus, after the fact.
For Josephus, please see my reply to JeremyP above. Josephus does, according to the vast majority of scholars, speak about Jesus, although there are also very likely Christian insertions into the text. As for Tacitus, here is what Annals 15:4 says,
"Consequently, to get rid of the report, Nero fastened the guilt and inflicted the most exquisite tortures on a class hated for their abominations, called Christians by the populace.
Christus, from whom the name had its origin, suffered the extreme penalty during the reign of Tiberius at the hands of one of our procurators, Pontius Pilatus, and a most mischievous superstition, thus checked for the moment, again broke out not only in Judæa, the first source of the evil, but even in Rome, where all things hideous and shameful from every part of the world find their centre and become popular. Accordingly, an arrest was first made of all who pleaded guilty; then, upon their information, an immense multitude was convicted, not so much of the crime of firing the city, as of hatred against mankind".
Are you suggesting that this does not refer to Jesus? If so, why, pray?
The Gospel writers are all in one source - the New Testament - of questionable provenance and with evidence that some of them copied others. You only have one source document.
Nope. See my reply to you above. We have one collection of documents, not one document (apart from the external sources of course).
As for "tampering", yes, there was some, but the question is whether we can get back to what the authors wrote. Ehrman in his appendix to "Misquoting Jesus", p252 of the American paperback edition, wrote, “Essential Christian beliefs are not affected by textual variants in the manuscript tradition of the New Testament.”
In the main, no that's not the question, because the overwhelming majority of Christians couldn't give a crap what the original might have been intended say, they have their opinion based on the modern poetic translation of the inaccurate Latin translations of the selectively edited Greek works which may or may not be the originals.
O.
And your evidence for this is what? Something you feel in your water or you read on some atheist website?