'Never accomplished' says who? Ac28, not God, not Christ, no Scripture!
You can't provide scripture that shows that they ever started it, let alone finish it. The Great Commission was to teach every creature and I must assume that includes Gentiles. The only Gentile any of the 12 ever ministered to, in the Gospels and Acts, was Cornelius, in Acts 10. by Peter, for the sole purpose of paving the way for Paul's ministry. Peter obviously hated every minute of it - it took 3 visions to get him to do it.
The Great Commission was given to the 12 (actually, 11 at that time) and to no one else. Certainly NOT to today's church. When it is finally accomplished, it will be done by the resurrected 12. Through Acts 12, there is little information about the 12 going anywhere. After Acts 12, most everything was about Paul. The goal during the entirety of Acts was NOT the great Commission and it was NOT to start a church. The ONLY goal was to convince Israel, as a nation, to repent and accept Christ. Why? Because Christ said in Matthew 23:39 , that He would not return until He was accepted by Israel. That also means that Israel's earthly Kingdom of Heaven would be postponed until Israel repented. The ONLY PUSH in Acts was to convince Israel to repent. The gifts of the Spirit were given because Israel requires signs. The Gentiles were allowed in to provoke Israel to jealousy, so they might repent. Everybody went to the Jew first, even Paul, the apostle to the Gentiles.
Had Israel repented in the Gospels or Acts, the New Heavens and New Earth would be about 1000 years old. Of course, the present day Gentile church would have never existed and the Gentiles would still be second class citizens (dogs, they were called), with no blessings at all of their own, from God, as their situation was from Gen 12 through the end of Acts, about 2000 years. Also, had Israel repented, today's Gentile church wouldn't have the Calling of spending eternity in the Highest Heaven, where Christ sits at the right hand of God, Ephesians 1:20 (Christ), Ephesians 2:6 (Us - same place). Today's Gentile church, found ONLY in Paul's 7 epistles written AFTER Acts, are the only people in the Bible to have a Hope of Heaven. Nothing in those other 59 all-Jewish is TO us, ABOUT is, or tells us anything about our future. Eph, Phil, Col, 1&2Tim, Titus, and Philemon are the only books in the Bible that are TO us, ABOUT us, and can tell us about our incredible future, which is infinitely better than anything ever given to Israel.
By the way, the Gentiles were never the people of God until Acts was over (1955 years ago) and Israel was set aside and haven't been God's people since, according to the prophecy in Hosea 1:9 and most all of Hosea. They will be Ammi, God's people, again, in about 45 more years The Gentiles have NEVER been under any part of the Law, nor have they ever been under the old or new covenants. Now, the first time we Gentiles have EVER been God's chosen people, we are under pure Grace. That means we are not under any laws or ordinances. Grace is the exact opposite of the works of the law. They can't co-exist.