I will agree that Jesus Christ was not God in the sense that he was God the Son. The bible refers to the body as a "holy thing" that "shall be called the Son of God" in Luke 1:35. Jesus was a vehicle for the Spirit to dwell in and to use. How that union worked together is what I would refer to Paul's teaching as the "mystery of Godliness" 1 Tim 3:16.
Why did Jesus cry out to God on the cross if he himself was God? Jesus was still flesh and blood like all of us and had to obey all the laws that we do too. Such as praying to God for deliverance. Whenever Jesus was on the Earth, he never claimed to be God nor did he decide to take any divine credit. In fact, when a man came to him and called him "good master" he deflected the response and said "there is none good but God". Mark 10:18
So, why do Christians claim that Jesus is God? Most Christians believe in a false idea called the Trinity, which, as you said, came from the council of Nicaea. This was a false idea spurred by the pagan beliefs of the regions around them and incorporated by the pastors of the churches. Paul called it a time of ravenous wolves. (acts 20:29) This Trinitarian belief has ruined many of the minds of Christians and non-Christians alike by presenting God as three persons AND making the Son and the Father one and the same, which they are not. Jesus Christ will eventually be put aside after everything is done and over with. (1 Cor 15) BUT for now, he has been given all power (Matt 28:18) and that power is not referring to divinity, but rather to the authority of his name through salvation.