I feel we should be hesitant about claims like this. It might well be true that Paul was the earliest writer.
But it also seems strange that Matthew, a presumably literate tax collector, wrote nothing at all before Paul despite being a disciple during the time Jesus was around.
Mind you I am only saying the earliest known writer, it's likely that most Christian writings are lost to history. And technically we don't even know who wrote the Gospels with any certainty. Only Paul's 7 undisputed letters are universally accepted by secular scholarship as being genuinely authored by Paul, the authorship of the rest of the New Testament is disputed.
There has never been a manuscript of a Gospel with anyone other than the traditional author attributed. And they’ve always been cited by the traditional names - even in Islamic, Jewish or heretical writings.
The arguments made in favour of Paul’s authenticity largely come from internal textual cues - but is that really more persuasive?
I don’t mean to suggest too strongly one side of the Gospel authorship debate over the other, only that these issues mix objective facts with subjective interpretation in a way that makes it very difficult to outsource to scholarly consensus.
Bible scholar Dan McClellan is on youtube and does short videos rebutting popular youtube/tiktok videos that make claims that aren't historical. Dan has said that the four names were not assigned to the texts until the second half of the 2nd century, probably around 180CE or so. That leaves 80-100 years where the books were in circulation before the naming convention was established.
The subject of authorship comes up frequently so he has addressed it a few times, but here is a short (under 7 minute) video. It isn't just an assertion, he gives reasons why he makes these claims:
There’s a big difference between the gospels not being cited by name directly, and not having a name. For example, the Gospels often cite Isaiah without using his name - just lifting direct quotes.
And there’re allusions to apostolic naming in things like Justin Martyr’s first apology, Ch67 (155CE, dating largely from it being co-addressed to Marcus Aurelius):
“ the memoirs of the apostles or the writings of the prophets are read, as long as time permit”
"Data over dogma." Dr. Dan McClellen is an engaging source for historically accurate interpretations and understandings of the bible. I encourage others to check his content out.
I am only repeating what modern scholarship has determined, wikipedia does far more justice than I could. Church tradition is far more assertive in authorship claims.
While Jesus is portrayed as extremely fluent in Jewish scripture, he's only ever shown to have written once and in the ground. Nothing exists indicating he ever wrote any works to be passed down. Some theologians theorize that Jesus purposely avoided writing due to parallels with the Old Testament's written laws that condemned man, while Jesus came to do the opposite.
I wouldn't expect God to go through the trouble of personally delivering his most important message then leave it to chance, knowing he wouldn't be around to answer questions and knowing nobody would write it down for decades, that only parts would survive, that there would be differences in interpretation. Knowing the fate of people who misunderstood.
Previously he wrote down ten commandments on stone tablets, and with his power he could easily write the most perfect book in a language everyone could understand that would leave no doubts as to what is required to be saved then ensure it survived forever. There would be no need for later writers on soteriology.
But it also seems strange that Matthew, a presumably literate tax collector, wrote nothing at all before Paul despite being a disciple during the time Jesus was around.