It is noteworthy that Paul has finished preaching the Gospel by the end of chapter 5. Beginning in chapter 6, he answers a series of rhetorical questions that address objections to the Gospel his readers will likely face as they return to Rome. Chapter 9 addresses a specific question about God's promise to Israel. We could formulate the question this way. Paul, your gospel can't be true because God promised to circumcise the hearts of all of Israel, and that hasn't taken place.
Short answer:
Paul’s opponents argue, “Your gospel can’t be true, Paul, because God promised to save all Israel — and clearly not all Israelites believe in Jesus.” Paul’s answer cuts deeper than they expect: God’s promise was never grounded in ethnicity but in election. Not all who are descended from Israel belong to the Israel of the promise. God has always defined His people by His own choosing, not by bloodline or national membership. So when God finally saves “all Israel,” it will be the Israel He has chosen, the ones whose hearts He circumcises by His Spirit. The promise stands firm — but it applies to the Israel God creates, not the Israel people assume.
I’m not sure I follow you entirely but I think I agree, so let me restate what I believe you mean: you believe Romans 9 is not about the leadership of the earthly nation of Israel, but instead, exclusively about spiritual Israel – the Israel of God - whose members are brought into it out of all peoples, kindreds, nations, and tongues, but only by God’s election of them through His mercy, and grace by Jesus Christ.