I don’t think your Acts 3 passage works for you like you would think. Peter wasn’t telling them the Jesus died for their sins. He told them He suffered just as their prophets had told them and that they needed to change that their sins may be forgiven just as they had been told throughout the Old Testament. And then look at verse 20 “and that he may send the Messiah, who has been appointed for you—even Jesus”. That he may “send the Messiah”? Peter was still talking about Jesus coming back as King and ruler in Israel.
Acts 3:
17 “Yet now, brethren, I know that you did it in ignorance, as did also your rulers. 18 But those things which God foretold by the mouth of all His prophets, that the Christ would suffer, He has thus fulfilled. 19 Repent therefore and be converted, that your sins may be blotted out, so that times of refreshing may come from the presence of the Lord,
The elements are all there, as Paul also confirms in 1 Corinthians 15. That the Christ was crucified, died, risen. Then the key words of "so that times of refreshing may come from the presence of the Lord."
How is that a kingdom gospel?
If Peter and the 11 preached only the kingdom gospel and Paul the Gospel of Grace, then at what point did Peter and the 11 shift from the kingdom message and take up the grace message?
Also, at what point did Paul cease teaching or preaching the kingdom gospel?
If Peter and the 11 preached a kingdom gospel on Pentecost what is it based on? The death and resurrection of Jesus Christ or promises of furthering the Law of Moses?
I also know you to be a man who studies God's Word. How many times do we correct people on this site for picking out pet theologies based on one or a few passages from a historical book as in Acts? Theologians consider Acts a historical recording of the events of the early church. My point is, if one wants to see what Peter preached in detail to Jews and Gentiles, they should look at his epistles. As many here keep quoting Paul's epistles, we should do the same for Peter.
1 Peter 1:
3 Blessed be the God and Father of our Lord Jesus Christ, who according to His abundant mercy has begotten us again to a living hope through the resurrection of Jesus Christ from the dead, 4 to an inheritance incorruptible and undefiled and that does not fade away, reserved in heaven for you, 5 who are kept by the power of God through faith for salvation ready to be revealed in the last time. 6 In this you greatly rejoice, though now for a little while, if need be, you have been grieved by various trials, 7 that the genuineness of your faith, being much more precious than gold that perishes, though it is tested by fire, may be found to praise, honor, and glory at the revelation of Jesus Christ, 8 whom having not seen you love. Though now you do not see Him, yet believing, you rejoice with joy inexpressible and full of glory, 9 receiving the end of your faith—the salvation of your souls. 10 Of this salvation the prophets have inquired and searched carefully, who prophesied of the grace that would come to you, 11 searching what, or what manner of time, the Spirit of Christ who was in them was indicating when He testified beforehand the sufferings of Christ and the glories that would follow. 12 To them it was revealed that, not to themselves, but to us they were ministering the things which now have been reported to you through those who have preached the gospel to you by the Holy Spirit sent from heaven—things which angels desire to look into.
Frankly, the above looks to be an expanded version of Peter's sermon in Acts 3. All the elements are there. In 1 Peter 1, Peter is teaching. In Acts 3 he is preaching. Luke is recording a historical event. He faithfully enters the key elements of the Christ's gospel message in Luke 24 in Peter's Acts 3 speech. Historians truncate, or telescope events to address key points.