Was Jesus of Nazareth a religious loon?

[Fake Messiah]

As for Paul, who shows little interest in the historical Jesus,

Really? He is writing pastoral letters, so he could be forgiven for not saying much about Jesus' history. But that's absolutely not the case- his writing is grounded in who Jesus was and what He did. For example, start right at the beginning Romans 1:

Paul, a servant of Christ Jesus, called to be an apostle and set apart for the gospel of God—  the gospel he promised beforehand through his prophets in the Holy Scriptures regarding his Son, who as to his earthly life was a descendant of David, and who through the Spirit of holiness was appointed the Son of God in power by his resurrection from the dead: Jesus Christ our Lord.

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.