Every one of the world’s faiths changed or added to the original vision of their founders.The "Kingdom Gospel" is not the same Gospel that Paul preached.
The Gospel that Paul preached is the Gospel that justifies the ungodly, Romans 4:5 and reconciles us and the world unto God, 2 Corinthians 5:18, 19.
Jesus did not preach that Gospel. He left it up to the apostles.
This is the way of all worldly things. It’s all about interpretations of human beings of the inspired interpretations of the biblical authors.