Perhaps you just overlooked these words of the Resurrected Jesus in Acts 9:15: "Go thy way, for he [Paul] is a chosen vessel unto me, to BEAR MY NAME BEFORE THE GENTILES, and Kings, and the children of Israel".
Paul had a special God-given mission to take the gospel to the Gentiles and the Romans were Gentiles.
St. Peter was the chosen one of God to take the gospel to the Gentiles.
"And when there had been much disputing, Peter, rising up, said to them: Men, brethren, you know, that in former days God MADE CHOICE among us, that by MY mouth the Gentiles should hear the word of the gospel, and believe.
Did God change His mind? I think not. St. Peter was above St. Paul in authority in the Church and sent St. Paul out as a helper to spread this message.
"Go thy way, for he [Paul] is a chosen vessel unto me, to BEAR MY NAME BEFORE THE GENTILES, and Kings, and the children of Israel".
What makes him MORE chosen than St. Peter or any of the other Apostles that spread and bore His name before Gentiles and the children of Israel?