You seem to have overlooked the phrase "And in this way".
No, I agree with you. Over and over throughout Paul's letters, he makes the point that there is no longer Jew or Greek, but only the body of Christ. It is the body of Christ that is true Israel.
I believe Paul, in Romans 9-11, is addressing his Jewish brother's and sister's concerns that God has tossed Israel to the side and broken His promises. So many Jews had rejected Christ, and yet, weren't they supposed to be the chosen people to whom belonged the covenant, adoption, glory, and promises?
Paul is explaining that no, the promises of God have not failed to natural (ethnic) Israel.
Romans 9:6
But it is not as though the word of God has failed.
Why have they not failed? Because not all natural ethnic Israel is true Israel
Romans 9:6
For not all who are descended from Israel belong to Israel
Paul uses Isaiah to show that only the remnant of natural (ethnic) Israel would be saved
Romans 9:27 And Isaiah cries out concerning Israel: “Though the number of the sons of Israel
c be as the sand of the sea,
only a remnant of them will be saved,
Again, does this mean God's word has failed natural (ethnic) Israel? No because only the remnant that is saved is true Israel.
It is this remnant of natural (ethnic) Israel and the grafted in gentiles that are true Israel.
Now in Romans 11:28-32, Paul is clearly making a distinction between the gentiles and natural Israel.
28As regards the gospel,
they (ethnic Israel) are enemies for your (gentiles) sake. But as regards election,
they (ethnic Israel) are beloved for the sake of their forefathers.
29For the gifts and the calling of God are irrevocable.
30For just as
you (gentiles) were at one time disobedient to God but now have received mercy because of
their (ethnic Israel) disobedience,
31so
they(ethnic Israel) too have now been disobedient in order that by the mercy shown to
you (gentiles) they (ethnic Israel) also may now
e receive mercy.
32For God has consigned all to disobedience, that he may have mercy on all.
Thereby when God saves only the remant of Israel, he is saving ALL of Israel because, not all of natural (ethnic) Israel is true Israel.
Again, he is addressing the concerns of his Jewish brother's and sister's who believe God has not kept his word in regards to natural ethnic Israel.