The Gospels are no more authoritative than the epistles...
While both are fabulous, I give a bit more credibility to the scriptures that were heard directly as Jesus was teaching during His time in a physical body on earth. Those words are the red letter words.
Paul did not meet Jesus while He was alive. Everything Paul received was through his connection with Jesus by going within, by reading the Gospels, or by speaking with people who heard Jesus first hand. Thus Paul’s writings do not include read letter words. While Paul’s writings were divinely inspired, I am not sure he was always a pure channel of Jesus’ thoughts as often Paul’s personal bias from formerly being a Pharisee came through. However, he also had great insights from Jesus that Jesus had not shared while in the physical body. Remember Jesus originally thought that His ministry was only for the Jews and His realization changed during His life.
Paul spent 3 years learning from the Risen Lord...