Does focusing on Paul's letters for Church Age truth mean the rest of the Bible is inappropriate?
No. For this age of grace, the Church Age, Paul is the designated Apostle of the Gentiles, so his letters give fundamental truths for salvation, the Christian walk, and local church operation. But that never implies the rest of the Bible is inappropriate; Paul writes all Scripture is inspired and profitable for reproof and instruction in righteousness.
Les teaches that focusing on Paul's letters for Church Age truth does not make the rest of the Bible inappropriate. He stresses that for this age of grace, the Church Age, Paul is the designated Apostle of the Gentiles, so the Pauline letters are where we garner the fundamental truths for salvation, the Christian walk, and the operation of the local church. But he immediately adds that this never implies the rest of the Bible is inappropriate—God forbid—because Paul himself writes that all Scripture is inspired of God and profitable for reproof and instruction in righteousness. In Romans especially, there is much that is fundamental for Gentiles, and that is the only reason they teach.