I think the writtings of Paul come from other sources like Philo and others . Many people say Paul was an imaginary character modeled after people like Saul of Tarsis and again his writtings were from other people. Experts have already deduced that half of the biblical writings attributed to Paul are forgeries.
Its amazing when you study heavily like your doing how most of the stuff in the Bible is not original to the Bible and it’s characters. Even some of the saying attributed to Jesus have been found to have been written many years earlier.