There doesn't seem to be much of anything actually substantiating King David's existence. Has this changed as of late? I know it's very important to modern-day Israeli historiography.
This is why the New Testament commences with proving Jesus's direct lineage from King David. Without it, Jesus is not the Messiah, and Christianity is baseless.
In any case, the basis of Christianity is that Jesus was God incarnate, died for the sins of the world, rose from the dead, and will come again to judge the living and the dead. Some early Christian polemic about interpretation of then-centries-old prophesy isn't core to that. It's a problem for fundamentalism, but that's an entirely separate issue.