That is the dispensational view, which in my opinion is wrong.
Like I said there is one gospel:
(Rom 1:16 For I am not ashamed of the gospel of Christ: for it is the power of God unto salvation to every one that believeth; to the Jew first, and also to the Greek.)
Rom 11 has no details to support your case. You just don't understand it correctly. Same with the dichotomy of claiming James is writing to some future generation of the 12 tribes, when in fact he was writing to the scattered of the 12 tribes of his own time calling them first fruits.
(James 1:1 James, a servant of God and of the Lord Jesus Christ, to the twelve tribes which are scattered abroad, greeting.)
(James 1:18 Of his own will begat he us with the word of truth, that we should be a kind of firstfruits of his creatures.)
And so does Peter write to the dispersed tribes:
(1 Pet 1:1 Peter, an apostle of Jesus Christ, to the strangers scattered throughout Pontus, Galatia, Cappadocia, Asia, and Bithynia)