A literal translation of those three verses is interesting. Young's Literal Translation does not use the word 'redeemed' in 1 Chron. 17:21; he says 'ransomed'. However, in 2 Sam. 7:23 he uses the word 'redeemed'. The key point does not seem to lie in differences between those two words for, in the context of those two texts, they seem interchangeable. But in Amos 9:7 he uses neither word (nor does the NSAB) so it might not be wise to think God has brought those other named nations to the same position of being ransomed unto redemption, as had he done with Israel.
It is right to point out that, in Amos, Israel is disparaged while those other nations appear to be lifted up by God. Yet those nations never become God's chosen nation; only if individuals from among the nations turn to the God of Abraham, Isaac and Jacob will they then become part of that called-apart nation, from God's point of view. That would entail becoming a proselyte, and the males being circumcised.
It is what the redemption of the nation of Israel is for that makes her unique. God has, indeed, had favourable dealings with other nations at various times, but he calls them to respect and honour him and his people, who are called by his name - a people meant to represent the holy God, the Creator. He also views those who do so as having - effectively - become children of Israel. Consider this Psalm where God is speaking:
"I will make mention of Rahab and Babylon to them that know me: behold
Philistia, and Tyre, with Ethiopia; this man was born there. And of
Zion it shall be said, This and that man was born in her: the the
highest himself shall establish her. The Lord shall count, when he
writeth up the people, that this man was born there." Psalm 87:4-6
A.V.
Now, Rahab was never born in Zion; neither were people from those other nations. Yet because God does not show favouritism, but in every nation the man that fears him and works righteousness is acceptable to him (Acts 10:35), we see that fact running as an unbroken thread throughout the Old Testament. Such individuals will be brought into the household of God.
Never lose sight of the other fact, however, that God punishes entire nations that rebel against him, and that hate him over a long period of time. He did that with his own people, Israel, for their continual idolatry and injustice. He raised up the nation of Babylon to break Israel's pride and rebellion. Then, after 70 years, he raised up other nations to destroy Babylon for going too far and rejoicing in being cruel to Israel. Reading the prophet Jeremiah, who lived at that time of Israel being destroyed by Babylon, we learn all of that.
Take, for example his chapter 47 where the land of Philistia, with Gaza, Ashkelon, Tyre and Zidon, are warned that God will raise up the Egyptians to destroy them. But later on, Egypt is warned that God will then raise up the Babylonians to crush them! And then the Babylonian empire will be smashed.
Those other nations are never 'redeemed' though times of long-suffering mercy be shown to them, by God. But Israel is unique in all the world for God choosing them to bear his name. Not because they are worthy, oh no! That prideful notion is given no ground, by God telling them shortly after being redeemed from the grip of Egypt, that they were the least of all the nations, both in numbers and in strength, but he called them by his grace, and according to his purposes.
I hope this helps to enlarge an understanding of those three texts.
