Where is this evidence that the earliest Christian writers said that Jesus was just an ordinary man?
To be clear: Just a man, rather than a virgin-born Son of the Holy Ghost. That was later.
The evidence is in the letters of Paul and the Gospel of Mark, which are the earliest Christian writings we have. I hope you will admit that the Gospel of Mark appears to portray Jesus as a man with a mother and brothers and sisters? So at least the Gospel of Mark supports this. Now on to Paul...
Paul's letters certainly say no such thing. As has often been pointed out here - Paul's letters describe Jesus as a supernatural spiritual scion of Yahweh in the heavens, who was known to Paul purely and entirely through divine revelation in the true meaning of ancient scripture.
Well, I'll show you mine and you show me yours.
(1) Paul calls Jesus "anthropos" (man) twice:
Rom 5:15 But not as the offence, so also [is] the free gift. For if through the offence of one many be dead, much more the grace of God, and the gift by grace, [which is] by one man [anthropos], Jesus Christ, hath abounded unto many.
1 Cor 15:20 But now is Christ risen from the dead, [and] become the firstfruits of them that slept.
21 For since by man [came] death, by man [anthropos] [came] also the resurrection of the dead.
Paul uses "anthropos" many times in his letters, and it ALWAYS means "human person".
(2) There are quite a lot of "seed of" statements as well. I'm not aware of any literature that has a non-human being being called a "seed of" a presumably living person. I won't go into them, but how do you read them in light of the contents of Paul?
(3) Romans 9:
Rom 9:3 For I could wish that I myself were accursed from Christ for my brethren, my *countrymen according to the flesh, 4 who are Israelites, to whom pertain the adoption, the glory, the covenants, the giving of the law, the service of God, and the promises; 5 of whom are the fathers and from whom, according to the flesh, Christ came...
Again, the obvious reading is Christ is a descendent of Jews. What is your reading of the above?
If you mean "son of God", then note that Paul says that any human can be a son of God in Rom 8:
Rom 8:14 For as many as are led by the Spirit of God, they are the sons of God.
So, over to you. How do you read the above? And can you show me where in the letters of Paul he describes Jesus as "a supernatural spiritual scion of Yahweh in the heavens"?