Honestly, I think the life of Jesus and his teachings are FAR more important than anything Paul said, yet many churches seem to be based more upon Paul than the gospels.
Jesus' words are obviously important, but Paul's are too.
Firstly, he was called by Jesus and filled with his Holy Spirit.
Secondly, he expanded upon Jesus' teachings, and ministry, and showed how to apply it. Note, I said "expanded upon", not "added to" or contradicted". Paul's epistles were written before the Gospels.
For example, Jesus said "this is my blood shed for the forgiveness of sins", Matthew 26:28. But how many of us would know that we have peace with God, Romans 5:1; are reconciled to God, Romans 5:11, 2 Corinthians 5:18; have been made alive with Christ and saved through grace, Ephesians 2:4-5; are heirs with Christ, Romans 8:17, Ephesians 2:6 and have been adopted as sons of God, Romans 8:16, Ephesians 1:4 - if it were not for Paul's writings?
Would we have teaching about the nature of love, 1 Corinthians 13:4-7; Romans 8:31-39, the resurrection of Christ and our resurrection bodies, 1 Corinthians 15, the gifts of the Spirit, 1 Corinthians 12:12-28, Romans 12:4-8, Ephesians 4:11 - as well as many other subjects, were it not for the epistles of Paul?
Since Jesus' teachings surpassed the Old Testament, is there any real reason to study it, other than for historical background?
Jesus' life, ministry, death, betrayal and resurrection are all prophesied in the OT.
The OT were the only Scriptures that Jesus, the disciples and the early church had, and they quoted from them often. The Gospel writers, especially Matthew, show how Jesus fulfilled OT prophecy.
Abraham being asked to sacrifice Isaac, who was saved at the last minute when Abraham sacrificed a sheep; foreshadows that God gave his Son, Jesus, the Lamb of God, as a sacrifice for us.
Moses saved the Israelites from slavery and death - and Jesus saved us from slavery to sin and spiritual death. The Passover meal was a prequel to the Lord's supper.
Through his written word, God has provided us with everything that we need.