I don't understand why you say "rather than" preaching the gospel. The gospel is the power of God for salvation to everyone who believes. They were converted by the gospel.
I suggest you are looking at this subjectively instead of objectively. The gospel is salvation to those who "believe". What does it really mean to believe. People have their ideas but God has seen fit to give us examples so we can read and understand what it looks like to believe the gospel.
If we look at the case of the Corinthians, Paul preached the gospel and what does it say about those who believed? In Acts 18:8 where they were converted by Paul we see that Crispus "the ruler of the synagogue, believed in the Lord". Crispus believed and we know that he was personally baptized by Paul.
If we continue with the verse we see And many of the Corinthians hearing Paul believed and were baptized. They heard the gospel from Paul and those who truly believed were baptized. I suggest to you that is what it means to believe the gospel. It doesn't say, many believe and some decided to get baptized. All the believers were baptized.
If you consider the question Paul asks the Corinthians in 1 Cor. 1, why does he ask it?
Or were you baptized in the name of Paul?
What is his point in asking this question?
"Baptized in the name of Jesus Christ", you say? Baptized with water, you say?
Let's look at what Paul says about the ONE BAPTISM that saves.
We are baptized "INTO JESUS CHRIST" (BY ONE SPIRIT)
1 Corinthians 12:13 For by one Spirit are we all baptized into one body, whether we be Jews or Gentiles, whether we be bond or free; and have been all made to drink into one Spirit.
BAPTIZED INTO HIS DEATH.
Romans 6:3-6 Know ye not, that so many of us as were baptized into Jesus Christ were baptized into his death? 4 Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life. 5 For if we have been planted together in the likeness of his death, we shall be also in the likeness of his resurrection: 6 Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin.
Your contention is that water baptism is the "operation of God" spoken of here? You notice the work on the heart. It all takes place the moment we believe. The Holy Spirit sees into the hearts of man. Man's lips can be claiming "I repent", and anyone can submit to being dunked, but only the Spirit sees the moment we are "begotten" by the Gospel.
Colossians 2:11-13
11 In whom also ye are circumcised with the circumcision made without hands, in putting off the body of the sins of the flesh by the circumcision of Christ: 12 Buried with him in baptism, wherein also ye are risen with him through the faith of the operation of God, who hath raised him from the dead. 13 And you, being dead in your sins and the uncircumcision of your flesh, hath he quickened together with him, having forgiven you all trespasses;
If you insist on calling water baptism the operation of God, then I give up. :nono: