There are actually a lot of good contemporary and modern writings on the 'Pauline Reinterpretation', or whatever it's called, where there are good reinterpretations from the Left of Paul's progressivism in order to reclaim his original thinking that was recuperated and reformulated by the conservative Church tradition. I really disagree with the usual Paul bashing and don't think Paul is as bad as people, both on the Right and the Left, usually think he is. It's funny because I meet a lot of Right-wingers that also hate Paul, but I think it generally comes from a lack of understanding. I don't think it's much different from how anarchists and Right-wingers both hate on Lenin, for example. Paul was pretty progressive, or even radical, for his moment and had a beautiful vision for Christianity.

And, historically speaking, it is absolutely necessary to include Paul's authentic letters in the canon as they are the earliest writings we have of Christianity at all. Paul's earliest epistle clocking at about 50 CE is about 20 years older than the earliest Gospel in the canon, the Gospel According to Mark which is estimated to be written in 70 CE. Although your statement that 12/27 books of the Bible are Paul's is factually incorrect as we now know that quite a few of the epistles attributed to Paul, and usually very conservative, are inauthentic. 12/27 books are Pauline but not necessarily Paul's. In fact, even his authentic letters are analyzed to have later interpolations that change the whole meaning of passages as well. Paul was butchered, in my opinion.

I don't remember all of the books on the subject, or even the term for it at the moment, but I would really recommend checking them out for a better grasp of the Pauline project. Taubes' The Political Theology of Paul, and Badiou's St. Paul are both great places to start and both leftist philosophers.