But I'm not sure we can verify, even, it was led by an apocalyptic prophet.

I completely agree - Paul is certainly apocalyptic, but something like the Gospel of Thomas has very different ideas, such as:

The disciples said to Jesus, "Tell us, how will our end come?"

Jesus said, "Have you found the beginning, then, that you are looking for the end? You see, the end will be where the beginning is.

Congratulations to the one who stands at the beginning: that one will know the end and will not taste death."

Jesus said, "Congratulations to the one who came into being before coming into being.

• Gospel of Thomas saying 18-19a

You see a similar notion opposed in the Epistles:

As to the coming of our Lord Jesus Christ and our being gathered together to him, we beg you, brothers and sisters, not to be quickly shaken in mind or alarmed, either by spirit or by word or by letter, as though from us, to the effect that the day of the Lord is already here.

• 2 Thessalonians 2:1-2

Among them are Hymenaeus and Philetus, who have swerved from the truth, saying resurrection has already occurred. They are upsetting the faith of some.

• 2 Timothy 2:17-18

(It's worth noting that while 2 Timothy is classically considered to be forged, it is the only disputed letter to have the same relative amount of personal reference as Paul's undisputed letters - he happened to talk about himself a lot like a covert narcissist is prone to, and that may offer another perspective on authenticity that's been missed by scholarship to date.)

There were no texts before Mark, as the movement was entirely word of mouth, and as per all games of telephone, evolved with each retelling.

That's a spurious claim based on an argument from silence and at odds with Papias's description of a sayings work we don't have, as well as a number of scholars estimating the date of a early core for the Gospel of Thomas, which Paul even seems to quote from as among the collection of resources in Corinth, potentially even as a written document.

Even an earlier form of Mark probably predated the version of Mark we have today. And the Pauline Epistles are documentary evidence that predate Mark (and likely even informed it).

What scholarly consensus does assert is the scripture is not univocal, inspired or inerrant, and the narrative bends with every era to affirm the morality of the time.

While the first part is true, the second is a gross oversimplification. The morals of some people at the time. For example, there was a massive women's speech movement going on in the first century that the church was opposing, including regarding women's speech in early Christian circles. So the scriptures that are misogynistic in the NT don't necessarily reflect the broader morals of the time so much as the reactionary morals of a select few controlling that version of the narrative.

Same with how Jesus was suddenly talking about marriage being between a man and a woman in a gospel whose extant version is dated after 70 CE, relevant to gay marriage having become an institution in Rome after Nero married two men in the 60s CE, but much less relevant in the 30s CE when he was allegedly saying it.

So keep in mind scripture only reflects morals of a select few of the time (and at the time of various edits).