Was Jesus of Nazareth a religious loon?

[Vicki Q]

The reference from your Wikiipedia article is from 2004, but, fine, then I am happy to reject the "scholarly consensus"! The scholar whom I trust, Professor Bart Ehrman, is the author of the following (now in its 7th edition):

The New Testament: A Historical Introduction to the Early Christian Writings 7th Edition

Can't recommend Professor Ehrman's writings enough!!

Yes- I've read that book and other writings by Ehrman, and I thoroughly agree with the recommendation.
Note that he did say:

Despite its wide-ranging differences from the Synoptics, the Gospel of John clearly belongs in the same Greco-Roman genre. It too would be perceived by an ancient reader as a biography of a religious leader: it is a prose narrative that portrays an individual’s life within a chronological framework, focusing on his inspired teachings and miraculous deeds and leading up to his death and divine vindication. (Ehrman, 2004, p. 155)

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Still there is not a single direct citation of Jesus’ teaching. In fact, in Romans 15:3-4 Paul all but tells us there are no stories about Jesus to draw upon – nothing but what we read about in the Jewish scriptures.

But then again it seems that Paul wrote those scriptures by looking at "secret" messages in the old Jewish writings and thus Paul himself invented Jesus(?)

Galatians 1:11-12   I want you to know, brothers and sisters, that the gospel I preached is not of human origin. I did not receive it from any man, nor was I taught it; rather, I received it by revelation from Jesus Christ.

Galatians 1:15-16  But when God, who set me apart from my mother’s womb and called me by his grace, was pleased to reveal his Son in me so that I might preach him among the Gentiles, my immediate response was not to consult any human being.

Some left field interpretations of Paul here.

Romans 15:3-4
3 For even Christ did not please himself but, as it is written: “The insults of those who insult you have fallen on me.”4 For everything that was written in the past was written to teach us, so that through the endurance taught in the Scriptures and the encouragement they provide we might have hope.
Not sure how v3 supports your case and v4 simply means that the Kingdom of God was promised in the OT, and now that God has delivered, the (much under pressure) Early Church should look to the future for hope and encourage .

Gal 1:11-12 Simply refers to Paul's conversion on the Damascus road, emphasising it was direct from Jesus rather than evangelism. Gal 1:15-16 He mentions his immediate response, yes, but read on to Gal 1:18 18 Then after three years, I went up to Jerusalem to get acquainted with Cephas and stayed with him fifteen days. So he got directly from Peter what Jesus said.

As for Paul not mentioning Jesus sayings, start with- 1 Cor 7:10-11 (cf e.g. Mark 10:11-12, Matt 5:32 note Paul differentiates his teaching from the teaching of Jesus), 1 Cor 9:14 (cf Matt 10:10, Luke 10:7), 1 Cor 11:23-26 (last supper).

Also note that Paul can mention sayings of Jesus, expect the Corinthians to recognise them and regard them as normative, can appeal to precise teaching Paul received after his conversion and imparted to the Corinthians after theirs (1 Cor 11:23, 15:3); all this argues for a fund of material from and about Jesus circulating amongst Gen1 Pauline churches.