Paul does not separate baptism from the Gospel. He separates the roles of preaching and baptizing, which is quite different from what you are claiming.
***Paul does not separate baptism from the Gospel***
1 Corinthians 1:17
For Christ sent me not to baptize, but to preach the gospel:
1 Corinthians 1:14
I thank God that I baptized none of you,
1 Corinthians 4:15
...for in Christ Jesus I have begotten you through the gospel.
Looks like a clear distinction to me.