The Tanakh is unambiguous that the deal is made between the Jewish nation and God, to the exclusion of everyone else; and also that a very particular symbol will always identify the Chosen, towit male circumcision.
Paul found that the requirement of circumcision was bad for sales, and is said by the author of Acts to have offered arguments against the requirement which, if you've read them, you already know are entirely specious and untenable. But such is politics that, at least as Paul tells it, he wins that part of the argument. Decades later, somewhere around 85 CE, the author of Matthew has Jesus declare that not a letter, not a dot, not a single coffee stain of the law shall be changed until the whole project is finished, which is entirely incompatible with the arguments which Acts attributes to Paul.
So Paul would use your argument, and the author of Matthew would reject it out of hand.
But the Christians have demonstrated their own view of your view by reviling, attacking, robbing, torturing and killing Jews for two millennia, and working on a third.
And the Jews would look like a single perfect whole compared to the Christians, who have split into two, then three, then thousands of different versions of Christianity, when in your story they'd be thinking of themselves as the unified homogeneous standard bearers of their own religion, let alone as some kind of unifying force for the three large Abrahamics.
I see two OT messages about the Gentiles
1 - the religion of the bible will be to both Jew and Gentile
2 - the religion will be to the Gentile
The Jews might believe the bible is theirs. This is why the townsfolk of
Nazareth tried to kill Jesus when he said only two people were helped
during a drought in Elias' day, both were Gentiles.
Jesus "came to his own" and that was His mission. The mission of his
apostles was to take that message to the whole world. And indeed,
Isaiah speaks of the Gentiles receiving the truth of God.
I wonder how many times Luke quoted from Matthew's Gospel, and
Luke died ca AD 66.
The Jews had a real issue in debating with Catholics and Protestants
over the centuries. If indeed the Jews are still God's people, literally,
then why are they in exile and their nation remains under the feet of
the Gentiles?
The issue of circumcision has no part in the New Covenant, like all
other symbols. This covenant, which many of the prophets said would
come, has no symbols other than baptism and the Eucharist. Peter
was wrong in these issues - he was still living in the Old Testament.
The doctrine of the New Testament is enunciated in Jesus' Sermon
on the Mount - it had nothing to say about the Law of Moses. Jesus
would say, "You have heard... but I say..."