I would say that we don’t accept your definition of sovereignty.
Sovereignty simply means that, in this case God, has the ultimate say so in every situation, and that no other power can overcome or overpower his decision.
I like to say that God, being Sovereign, is not subject to our rules, he plays by his own rules. We see this time after time in the OT, such as with Jacob and Esau. Man’s rules say the oldest son gets the inheritance, but God says no, the older will serve the younger. Those are God’s rules. We see the same thing with David being exalted to being the King of Israel over his seven older brothers.
In Romans 9-11, Paul is, on the one hand, dealing with the Jewish brothers feeling left out because God let the Gentiles in and they now controlled the local church, and one the other hand, that the Gentiles were feeling superior to the Jews because they believed and the Jews, as a whole, didn’t believe in Jesus.
The Jews thought the rules said “salvation is of the Jews, therefore, they are first and more important, but God said my rules say that if the Jews won’t believe, that he will “go to a people who are not a people”, the Gentiles who will believe. Why, because he is sovereign and he makes the rules that he plays by, and it’s not our rules.
God set them both straight and said if the Jews would believe that they would be grafted back into the tree from which they were cut off, and that if the gentiles were to stop believing, that they too could be cut off just like the Jewish “natural branches”.
God has mercy on those in whom he finds belief, and he hardens those in whom he finds rebellion. Man’s rules do not establish the criteria of mercy, but God’s rules!
Doug