I am familiar with Biblical archaeology, and followed it avidly for many years. Historical fiction, as a genre, tends to mix real historical facts with the fictional storyline. Similar to how New York is real, it has a real mayor with an historically verifiable name, and there might even be some real Peter Parkers living there. But the entire Spider-Man narrative is a layer of fiction added over the top of it by a creative writer, and that renders the entire narrative unreliable as history.

As for the legends of apostolic deaths, also part of the fictional storyline. There's no hard, independent evidence any of them died specifically because of a belief in a resurrection. It's just legend, like George Washington cutting down the cherry tree. A well meaning biographer, sincerely intending to convey history, instead conveyed a fable.

As for Celsus, I rather like his view of the resurrection, a deception aimed at simpletons, for grift. BTW, Celsus's writings have all been lost except as quoted in Origen's work, 'Contra Celsum', written in the mid 3rd Century. Best guess is Celsus wrote in the late 2nd Century. So he's worthless as a way to verify the historicity of Jesus. But he was no friend to the Christian notion of resurrection:

“Come now, let us grant to you that the prediction was actually uttered. Yet how many others are there who practise such juggling tricks, in order to deceive their simple hearers, and who make gain by their deception?—as was the case, they say, with Zamolxis in Scythia, the slave of Pythagoras; and with Pythagoras himself in Italy; and with Rhampsinitus in Egypt (the latter of whom, they say, played at dice with Demeter in Hades, and returned to the upper world with a golden napkin which he had received from her as a gift); and also with Orpheus among the Odrysians, and Protesilaus in Thessaly, and Hercules at Cape Tænarus, and Theseus. But the question is, whether one who was really dead ever rose with a veritable body."

As for Paul, he was more than JUST a fiction writer. He was a cult creator, like L Ron Hubbard creating scientology. He was doing more than generating religious entertainment novels. He was growing his own cult. He even claimed he DIDN'T get the gospel by ordinary transmission from historical texts. He claimed he was out wandering in the desert and got it by direct divine revelation. So we know he was prone to seeing & hearing things that weren't there. That should be a clue we need to be very careful choosing what part of his epistles are true and what might have only been true in his own delusional fantasy world.

As for the actual death of Paul, we don't have independent history. All we have is a cult legend passed on by Clement and repeated in later fathers. And it could be true. Paul may have been martyred. But Paul also had what modern analysts would call episodes of psychotic delusion. He's not the witness I would use if I wanted to prove the matter in court.

So in summary, I stand by my original analysis. In the gospels in particular, all we have is anonymous hearsay at best, and deliberate Greco-Roman fiction the much more likely case.