My short answer is: I don't think Rom. 11 is by Paul. The chapter is missing in the version that Tertullian knows from the collection of Marcion's Paul. I think, chapters 9-11 has been added after the Bar Kokhba war, when Paul's collection of letters became part of the broadened NT with the four Gospels, Acts asf. It had been developed out of the few quotes from chapter 10 that were also present in Paul's Letter, as found by Marcion. The entire problem of the relation between Christian and Jews became reflected by Christians during and after that terrible revolt and war, as can also be seen from the number of apologies that Christians wrote, and where they start to discern between them and Jews, between them and Greeks and others (though rarely between them and Romans!).
The NT, as we know it, and the Pauline Letters in the version that we find today in our critical editions veil this novel approach by Christians during the second century, particularly, as this version is then taken by late second century authors like Irenaeus as the basis of their own vision of the beginnings of Christianity, a topic which is set out in more detail in my recent book "Offener Anfang" which will be published in an English version in the coming year with Cambridge University Press.