I think the gospel of the first Christians (a la the Corinthian Creed that Paul received from them) was that humankind had become reconciled to God through the atoning sacrifice of Christ. Maybe what made Jesus the anointed one for the first Christians was not that he was going to overthrow Roman rule, but that he had atoned for the sin debt of mankind and hence it was the end of the world and he was the “first fruits" of the general resurrection. Maybe after Jesus died some of his followers had visions of him, and searched scripture for what that meant. Maybe they came upon Isaiah 53 about the suffering servant and that “by his stripes we are healed," and so thought this is what Jesus’ death meant – that his death paid for our sins. We know the first Christians thought Jesus’ atoning death and resurrection was prefigured in scriptures, since Paul said “3For what I received I passed on to you as of first importance: that Christ died for our sins according to the Scriptures, 4that He was buried, that He was raised on the third day according to the Scriptures,… (1 Cor 15:3-4)." We know that it may have been prefigured in scripture (or the first Christian thought it was prefigured in scripture) that there would be some suffering to overcome Satan, because scripture says " He shall bruise you on the head, And you shall bruise him on the heel (Genesis 3:15)." We know that for the first Christians Jesus atoning death signalled the beginning of the end and the advent of the general resurrection, since Matthew said after Jesus died that “…51At that moment the veil of the temple was torn in two from top to bottom. The earth quaked and the rocks were split. 52The tombs broke open, and the bodies of many saints who had fallen asleep were raised. 53After Jesus’ resurrection, when they had come out of the tombs, they entered the holy city and appeared to many people.… (Matthew 27:51-53)." Mark’s portrayal of the death of Jesus was one of reconciling humanity to God through atonement. Upon Jesus’ death, the tearing of the veil of the temple symbolized the removing of the barrier between people and God. The words of the Roman soldier that “Jesus was truly the son of God" symbolized the reconciling of the differences between Jews and Gentiles. The women being the witnesses to the empty tomb reflected the eroding of the inferior place of women and the unreliability of the testimony of women in the eyes of God. Hence, on this point, Paul also said “There is neither Jew nor Gentile, neither slave nor free, nor is there male and female, for you are all one in Christ Jesus (Gal 3:28)."
None of this required Jesus to be a God.