What does Paul's greeting 'to all the brethren who are with me' in Galatians subtly indicate?

Paul’s greeting “to all the brethren who are with me” subtly indicates how far the Galatian churches had already degenerated because of a perverted gospel. It shows that the churches of Galatia had drifted from the gospel, so Paul included the brethren who were with him in the greeting alongside the churches of Galatia.

Les teaches that Paul is writing to all the brethren who are with him unto the churches of Galatia, and this is a subtle way of telling us how far these Galatian churches had already degenerated because of a perverted Gospel. He then points to Romans 1:7, where Paul calls the Romans beloved of God and called to be saints, which is quite a commendation. He also notes 1 Corinthians 1:2, addressing the church of God at Corinth as sanctified in Christ Jesus, called to be saints, and with all in every place calling upon the name of Jesus Christ our Lord. These greetings help show the Galatians’ condition.

Galatians 1:2

And all the brethren which are with me, unto the churches of Galatia:

How does Paul address the Galatians compared to other churches?

Paul addresses Corinth as the church of God with all the saints, and Ephesus as the church of God and the faithful in Christ Jesus. To the Galatians, however, he writes only to the churches of Galatia, omitting designations like church of God, saints, or those in Christ.