But Paul did not preach to the Jews, he preached to the Gentiles
He did both, but no matter the audience, that does not change that salvation is from the Jews.
Paul went first to the synagogue in every city he visited.
And on the sabbath day they went into the synagogue and sat down. 15 After the reading of the law and the prophets, the rulers of the synagogue sent to them, saying, “Brethren, if you have any word of exhortation for the people, say it.” 16 So Paul stood up, and motioning with his hand said… Acts 13
17 Now when they had passed through Amphip′olis and Apollo′nia, they came to Thessaloni′ca, where there was a synagogue of the Jews. 2 And Paul went in, as was his custom, and for three weeks[a] he argued with them from the scriptures, 3 explaining and proving that it was necessary for the Christ to suffer and to rise from the dead, and saying, “This Jesus, whom I proclaim to you, is the Christ.” Acts 17
Paul taught the Jews in the synagogue from the “law and the prophets” that were read every Sabbath. He used the Septuagint to prove that Jesus is the Christ.
St. James wrote to the Christians on the foundation that Moses is taught in the synagogue.
"For from early generations Moses has had in every city those who preach him, for he is read every sabbath in the synagogues.” Acts 15.
Why would it be relevant for the Christians to have Moses preached in every synagogue on the Sabbath if what Moses had to say was not relevant?
If you think that Paul did not preach to the Jews you have missed some significant portions of the book of Acts!
No one could be saved by Jesus in the Old Testament because Jesus wasn’t born yet.
God’s plan of salvation has not changed. He has made Jesus the only name under heaven by which we may be saved. This is why the holy souls of the OT waited for Him.
Even Abraham could not get into heaven right away because Jesus had not yet paid the price for all sin yet.
Now you are beginning to get the picture. All the holy souls waited to see the day of Christ, so that the gates of heaven would be open, and they could enter.
The teaching may have eventually be corrected
No, this was just a bad practice, never a teaching of the Church. Clerics acting badly do not equate to Apostolic Teaching, which is preserved infallibly in the Church by the Holy Spirit.
present to the mass as the will of God through the church.
Sadly there have been many misdirected ideas over the course of history that have been presented to people as the will of God. This does not make them teachings of the Church. They are just the product of wolves in sheeps clothing.