All the thief on the cross proves is that Jesus could cleanse that man of his sins. What Jesus did for the thief he did not do for us. He took the thief’s sins away before He died. Everyone coming after the cross must come into contact with the blood of Christ Jesus through baptism.
You're making it up as you go along.
The thief on the cross is not the only example of a person who was saved and was not baptized.
Luke 19
1 He entered Jericho and was passing through.
2 And there was a man called by the name of Zaccheus; he was a chief tax collector and he was rich.
3 Zaccheus was trying to see who Jesus was, and was unable because of the crowd, for he was small in stature.
4 So he ran on ahead and climbed up into a sycamore tree in order to see Him, for He was about to pass through that way.
5 When Jesus came to the place, He looked up and said to him, “Zaccheus, hurry and come down, for today I must stay at your house.”
6 And he hurried and came down and received Him gladly.
7 When they saw it, they all began to grumble, saying, “He has gone to be the guest of a man who is a sinner.”
8 Zaccheus stopped and said to the Lord, “Behold, Lord, half of my possessions I will give to the poor, and if I have defrauded anyone of anything, I will give back four times as much.”
9 And Jesus said to him, “Today salvation has come to this house, because he, too, is a son of Abraham.
Now, what is it that happened here? Clearly Zaccheus understood who Jesus was ... he demonstrates true repentance in that he was willing to make restitution. But he was not baptized ... and what did Jesus say to him. "Today salvation has come to this house ..."
It is not baptism that causes salvation ... it is repentance, faith, and calling on Him as Lord.
Want another example? The seventy ...
After they came back they said ... Luke 10
17 “Lord, even the demons are subject to us in Your name.”
18 And He said to them, “I was watching Satan fall from heaven like lightning.
19 Behold, I have given you authority to tread on serpents and scorpions, and over all the power of the enemy, and nothing will injure you.
20 Nevertheless do not rejoice in this, that the spirits are subject to you, but rejoice that your names are recorded in heaven.”
I can keep going ...
The point is this ... in mathematics, when you postulate a theorem ... all someone needs to do is provide one counterexample to the theorem and that theorem is disproven. Baptism is not a requirement for salvation ... there are many examples in the Bible.
Theology flows from the text ... not the other way around. Theology doesn't flow into the text.
What Jesus did for the thief he did not do for us. He took the thief’s sins away before He died.
The Bible teaches otherwise ...
Colossians 2:13-14
13 When you were dead in your transgressions and the uncircumcision of your flesh, He made you alive together with Him, having forgiven us all our transgressions,
14 having canceled out the certificate of debt consisting of decrees against us, which was hostile to us; and He has taken it out of the way, having nailed it to the cross.
Notice ... having forgiven (past tense) all our transgressions ...
Now correct me if I'm wrong but the Colossians were ALIVE at the time Paul wrote to them ... and your second assertion has been disproven as well.
Perhaps you should consider a NT read through ... apart from the readings in mass, where you get a morsel not a meal. Go feed yourself ... read the gospels and the epistles in context ... and perhaps God may grant your eyes to be opened to the truth.
Everyone coming after the cross must come into contact with the blood of Christ Jesus through baptism.
As I have repeatedly demonstrated, the text of the NT teaches otherwise ... it doesn't happen through baptism ... it happens by repentance and faith in Jesus Christ and calling on Him as Lord. Read the entire NT and perhaps you will see that. Repent from dead works ... and yes, repent from false doctrine.