A link to one or more of these "authorities" would be appreciated.
Wiki give this:
The Deutero-Pauline Letters by Felix Just, S.J., Ph.D.
Carrier also gives physical books as references in OHJ for this which ironically two of which are authored by the person one of the original threads was about: Ehrman.
They are
Forged 2011 and
Forgery and Counterforgery 2014
There are also relevant chapters by Ehrman in
The New Interpreter's Bible 2006
We also get I Michael White
From Jesus to Christianity
These are just the tip of the general consensus.
For "Paul" to have been a genuine living human being, and not a fictional character, one need only furnish an account of his life, from a source not affiliated with the church. There are several Greek and Latin historians of the first two centuries. Justin Martyr isn't the only one who fails to mention "Paul". I simply find it odd, that someone of such supposed significance, should have zero attestation from anyone, until the end of the second century.
The problem with this as I pointed out before using material from James Burke's
The Day the Universe Changed (1985) (as Carrier's book wasn't averrable at that time as a handy reference) is that Christians themselves were the ones preserving much of this material.
To be fair to the Christians the hand copying of works was a tedious process where just one book could take a year to copy. So they had to be selective about what they copied; they simply could NOT copy everything. Also what they had to copy varied from monastery to monastery.
Even when the Christians did bother to copy something you had the problems of actually knowing it was copied and where it was.
There wasn't enough knowledge in any one monastery to separate the works into separate subjects or categories. Texts had their titles inscribed on page edges or on the first page of the book, and those titles often said little about the contents of the text. Worst of all the "library" was more often then not a spare room where anything extra got dumped a "medieval Higgledy-piggledy" as Burke puts it. Burke's example,
Sermones Bonventurae (Sermons of St. Bonaventure) shows just what kind of mess things were. This book could be
Sermons composed by St Bonaventure of Fidenza
Sermons composed by somebody called Bonaventure
Sermons copied by a Bonaventure
Sermons copied by somebody belonging to church of St. Bonaventure
Sermons preached by a Bonaventure
Sermons once owned by a Bonaventure
Sermons once owned by church of St. Bonaventure
Sermons by various people of whom the first or most important was by somebody called Bonaventure--the rest of the book? No clue.
In fact, things were such a mess than many works were "saved from the mildew and the rats" only because Renaissance got an interest in the Classical world and was going after any copy of Greek and Roman works they could get their hands on. One man (Aldus Manutius) made it his mission to publish every Greek classic known and it thanks to him that we have as much as we do regarding the ancient myths, stories, and accounts of the Greeks and Romans as we do.
Even with this mammoth endeavor the Renaissance publishers missed works that were found centuries later. For example, Books IV–X of Hippolytus'
Refutation of all Heresies was found in a monastery of Mount Athos in 1842!
So even if some monastery had works regarding the mundane life of Paul and deciding copying it was a good idea you have the issue of them even knowing they had it to continue to preserve it. On top of that not all monasteries survived to the time of the Renaissance to be preserved via printing and as seen with Hippolytus even then they didn't get everything.
So this idea that 'there is nothing non Christian on Paul so he is fiction' is nonsense.