Your claim in the thread title is not a realistic claim. If you're not seeing what our Lord Jesus preached and what His Apostles preached as the same... Gospel, then it is because you are not understanding what all is contained in The Gospel of Jesus Christ, and/or instead have allowed men's leaven to creep in.
God's promise to David about one sitting on his throne unto all generations is a mystery. David's throne is still manifested here on earth today, but not in Jerusalem, and it is established in the Gospel of Jesus Christ, literally not just spiritually. If you're not aware of that it means you haven't yet understood about God's Birthright promises that began with Abraham, and continued to Ephraim and Manasseh, whom it still continues among today:
1 Chron 5:1-2
5:1 Now the sons of Reuben the firstborn of Israel, (for he was the firstborn; but, forasmuch as he defiled his father's bed, his birthright was given unto the sons of Joseph the son of Israel: and the genealogy is not to be reckoned after the birthright.
2 For Judah prevailed above his brethren, and of him came the chief ruler; but the birthright was Joseph's
KJV
Genesis 49:10 is another Scripture proof that David's throne is still manifested here on earth with one of the house of David sitting upon it, which is to continue like that until Jesus returns (rendered as "Shiloh" there).
Our Lord Jesus in Matthew 21 revealed the kingdom would be taken from the unbelieving Jews in Jerusalem and instead given to a "nation" that would bring forth the fruits of the vineyard. Those fruits represent the spread of The Gospel and those who would believe, of both Israelite and Gentile, and they would become one body under Christ Jesus.
And that reign over nations has historically been true with what peoples after God ended David's throne in Jerusalem back in Jeremiah's day? With the western Christian nations under The Gospel. This has been true historically especially at the height of colonial rule by the western Christian nations. The Christian west are financially bailing out poorer nations still, lending them monies. Can't apply this to the Jews either, for the state of Israel in the middle east no longer existed when this happened since the Romans destroyed it in 70 A.D. The Christian nations were instrumental in helping the Jews to re-establish their nation state of Israel in the middle east in 1947.
Not just the believing remnant of Israel will possess the kingdom but also the believing Gentiles, together 'with' Israel. Christ's Church is made up of both, together, as one body. Both inherit together.
John Nelson Darby with his Dispensationalism was instrumental in hiding this, since he falsely taught that at Christ's return Israel is a separate restored kingdom on earth while Jesus and His Church reign from Heaven. Darby and et al, created that idea to help drum up support for the Pre-trib Rapture theory.
That is not the proper interpretation of what Jesus said. When He said He was not sent 'but' unto the lost sheep of the house of Israel, He was pointing to the ten scattered tribes of the "house of Israel" that were not... even present in the holy land at His 1st coming. Your interpretation doesn't even recognize the Bible history about God's split of the old kingdom of Israel after Solomon's days (see 1 Kings 11 thru 2 Kings 17). After that happened only the ten northern tribes of Israel were known as the "house of Israel". The southern kingdom of Judah was known as the "house of Judah" (Jews). Not long after that split, which was long before Jesus' 1st coming and Ministry on earth, the majority of the ten tribes were still scattered beyond Euphrates.
So what did our Lord Jesus really mean with that Matthew 15:24 prophecy? Easy. He, meaning The Gospel, was actually sent to the scattered ten lost tribes, i.e., the "house of Israel" that was scattered among the Gentiles, and they along with the Gentiles would believe. Did this literally happen after the majority of Jews in Judea rejected Jesus? You bet it did! The nations where Christ's disciples preached The Gospel after His death and resurrection began to put away their idols and became the Christian nations of history! And it was a miraculous transformation. So by the idea of His being 'sent', it pointed to the receiving of The Gospel. Since Apostle Paul in Romans 11 showed God had blinded the Jews in Jerusalem so The Gospel would go to the Gentiles, it is the same kind of idea. Thus The Gospel had to be preached first at Jerusalem, but God's Plan wasn't that they would be the main ones ordained to receive it.
Thus our Lord Jesus was actually confirming The Gospel going to the nations.
So didn't this happen when the lost sheep of the house of Israel received Christ Jesus along with Gentiles they were scattered among? Yes, it did. So to treat believing Israel as a separate body from Christ's Church is un-Biblical. Christ's future Kingdom on earth is about His Church. The deceived like Darby, Scofield, et al, on the Pre-trib Rapture are confused about this and teach against written Scripture.
(Cont.)