> ... most of the new testament has him [Jesus] as a fully separate person with his own separate agenda ...
Just want to correct a couple errors of fact here, by quoting from the sources that you're misunderstanding.
"And he withdrew from them about a stone’s throw, and knelt down and prayed, saying, 'Father, if you are willing, remove this cup from me. Nevertheless, not my will, but yours, be done.'" - Luke 22:41-42 (copied from https://biblehub.com/esv/luke/22.htm)
He doesn't want to suffer and die on the cross. Yet he chooses to serve the Father's agenda, not his own.
"I and the Father are one." - John 10:30 (copied from https://biblehub.com/esv/john/10.htm)
And note that, if you read just a few more sentences, you discover that this statement caused the Jews listening to him to pick up stones to stone him (for anyone who doesn't know, stoning was a method of execution: they intended to kill him). He asks (verse 32) why they want to stone him, and they reply (verse 33) that it's for blasphemy — "because you, being a man, make yourself God."
Finally, I want to address one other point in what you said:
> Christianity, if you ask anyone besides a christian, is polytheistic.
It's true that if you ask most people who are not Christians, most (not all, but most) will tell you that Christians worship three gods. But consider this: if you want to find out about Buddhist teaching, who would be a better source for explaining it to you correctly, a Buddhist, or a non-Buddhist? If you want to find out about Jewish teaching, who would be more informed about it, a religious Jew, or a non-Jew? (The word "Jew" is ambiguous, referring to both a religion and an ethnicity — so I use the term "religious Jew" to distinguish people who follow the religion from people who are ethnically Jewish but don't follow the Jewish religion). If you want to be well-informed about Islam, who would explain it to you better, a Muslim, or a non-Muslim? And if you want to understand what Christianity actually teaches, who's more likely to be correct about it, a Christian or a non-Christian?
P.S. To explain just a little further, the teaching of the Trinity is indeed one of the most complex teachings of Christianity to fully grasp, and there have been countless arguments and debates about it over the centuries. The council at Nicaea in AD 325, which formalized the Nicene Creed, did not completely settle that — some people continued to argue over the doctrine later — but it pretty well cemented the official church position. That the Father, the Son, and the Holy Spirit ("Holy Ghost" in older English texts, but "Holy Spirit" in modern English) are both three and one. The modern English translation of the Nicene Creed is probably worth quoting here (at least the relevant bits) so people can see what the actual teaching is:
"I believe in one God, the Father almighty ... I believe in one Lord Jesus Christ, the Only Begotten Son of God, born of the Father before all ages. God from God, Light from Light, true God from true God, begotten, not made, consubstantial [which means "of one being, of one nature"] with the Father ... I believe in the Holy Spirit, the Lord, the giver of life, who proceeds from the Father and the Son, who with the Father and the Son is adored and glorified ..." (Source: https://www.usccb.org/prayers/nicene-creed, though there are multiple translations, e.g. the translation I'm most familiar with says "of one being with the Father" rather than "consubstantial with the Father").
And before I quit writing this P.S., I want to mention one kind of awesome story about the council of Nicaea. Which is the story about what St. Nicholas allegedly did there. (Yes, the St. Nicholas whose life inspired the story of Santa Claus). Sadly, the story is probably not true, since Nicholas's name does not appear in any of the lists of attendees that have survived... but it's an awesome story anyway. The story goes that Arius was standing in front of the council arguing his position, which was that Jesus had not existed eternally, but was created by God the Father at one point. (The famous phrase is "There was a time when he was not".) That part is certainly historically true. What is likely not historical is the rest of the story: that Nicholas got so mad at Arius's denial of the divinity of Jesus that he got up and slapped (some sources say "punched") Arius in the face.
Which leads to this historical-humor variation on a famous American Christmas carol:
He knows when you are sleeping,
He knows when you're awake,
He knows when you've denied the divinity of Christ,
So if you're an Arian, DUCK!
P.P.S. One last note. My intention here is not to argue, but to explain. I am happy to argue/debate with anyone who wants to discuss further, but HN is not the right place for
literal religious debate. If you want to argue or debate about Christian teaching, feel free to contact me at (my HN username) at pobox dot com. (And if you just write a note here that you've done so, that will avoid the possibility of my missing your email: my pobox address gets a lot of email).