For starters, while Mark is considered the first Gospel written, the letters of St. Paul are the earliest Christian writings and St. Paul referred to the divinity of Jesus. So it would be a bit disingenuous to claim Mark represents the earliest Christian theology.
As for the Gospel of Mark, it clearly makes a case for the divinity of Jesus. Mark has John the Baptist referring to Jesus as the coming of the Lord (Mark 1:3). Jesus says that he is “Lord of the Sabbath” (Mark 2:28) which can only be a reference to divinity. Jesus also speaks throughout the Gospel of Mark with authority, Jesus does not debate or discuss matters of religion but instead pronounces the answer. That would be unlike any other human religious leader of the time. If Jesus is not divine, then how could the Transfiguration have taken place? And why would a mere human be able to walk on water? Jesus, of his own authority, casts out demons, heals the sick, and calms storms. All those are divine actions.
As to whether or not there is a resurrection account in Mark is open to debate. However even scholars who reject the resurrection account as original to the Gospel do not hold that Mark rejected the resurrection. Jesus predicted his resurrection in the Gospel of Mark (8:31; 9:31; 10:34). Of those who reject the resurrection accounts in Mark, it is generally accepted that the Gospel ends at 16:8 with the empty tomb. There two possibilities. Either the verses following 16:8 were lost along the way or Mark was giving us a theological challenge. Mark took great pains in his Gospel to show the authority of Jesus and his uniqueness. Jesus proclaimed that he would be resurrected, the question is: do we believe him? Mark may have concluded his Gospel with the empty tomb as a symbol that we all stand at the empty tomb challenged with whether we believe the words of Jesus or not.
We have to remember that in the first century AD there were no bookstores. Things were not written down for mere general consumption, plus not many people could not read. Books were written for specific groups or communities. The Gospel writers were writing to a specific audience to address their specific issues and concerns. If the community that Mark was writing to did not question the divinity of Jesus then he would have no reason to emphasize it. That is why we have 4 Gospels and numerous letters from Paul and other disciples. Each book and author of Scripture have something to say, but they were each written to address a specific community and specific issues. That is why we have to take Scripture as a whole and not cherry pick verses to prove a preconceived point.