RE Romans 11. The question is Who Is Israel, which is the subject of the OP. It’s not natural, genetic Israel. It is the Israel of God, which is all believers in Christ in addition to a remnant from the Old Covenant (11:5).
The Arabs thought it was a clever trick and used it one more time to make Mohamed and Islam the true replacement for Christianity.
Historically this view has led to a lot of nasty anti-Semetism.
For instance the Protestant sect's inventor Martin Luther came to hate the Jews for not acknowledging Christ as the repacement leader and went on to suggest something akin the the Nazi Nuerenberg laws. It's not really surprising the Holocaust was perpetrated by the Government of the country that venerated the antiSemetic heritic.
Supernatural claims to have superseeded someone's religions are always an ungly thing and should be avoided by thoughtful people.2