John was not a Christian, strictly speaking, and he baptized a lot of people, including Christ himself. Also, the verse says "water AND the Spirit". Important distinction.
That's the usual way. If the thief on the cross next to Jesus was ever baptized, we don't know about it, yet he made it into the Kingdom by faith and by the words of Christ.
If we're going to use the thief on the cross as the definitive example of the way to salvation, then it seems to me we ought to at least acknowledge in his example the title given him as part of that distinct example - i.e. the thief
"on the cross" and recognize if the thief IS an example then BOTH his expression of faith AND his having actually died with Christ are relevant.
Of course, to use his example thus it becomes immediately evident how problematic his example is insofar as he is the ONLY one in history to have actually physically died with Christ.
Paul solves this obvious dilemma though by giving us a definition of Christian baptism in Romans 6 -
"...do you not know that all of us who have been baptized into Christ Jesus have been baptized into His death? Therefore we have been buried with Him through baptism into death, so that as Christ was raised from the dead through the glory of the Father, so we too might walk in newness of life..."
Then there are Jesus' commands in Mark 16:16 and Matthew 28:18ff which I daresay He meant.
Then there is Peter's response to those he'd just convicted of crucifying Jesus in Acts 2:38ff.
Then there are the examples in Acts of people becoming Christians - the Ethiopian eunuch in Acts 8, Paul's own conversion in Acts 9, Cornelius' conversion at the end of Acts 10, Lydia's conversion in Acts 16, the jailor's conversion at the end of that same chapter, and so on.
Then there is the question of where, Scripturally, we are told when and how we receive the gift of God's Holy Spirit to dwell in us? Cf. Acts 2 again and Acts 19.
I think it very dangerous to imply (and even more dangerous that anyone would dare teach) that baptism is unnecessary - for to do so is to contradict Jesus' commands, Peter's answer, Paul's explanations, and Luke's numerous examples.
Denominations can wrangle about the mode, the timing, the purpose, whether it's a "work" or not, etc. and etc. - and they've been doing so for centuries, but about it's importance and necessity? I don't think there's any room for wrangling there - least wise not on the pitifully weak example of the one person in history who actually
was crucified with Jesus. If anything, his example ought to drive us all to our knees for some substitute opportunity to be able to experience what he, and he alone experienced - the opportunity to actually be crucified with Jesus, that we might walk in newness of life too like he'd been promised.
What IS "required" for salvation?
Faith certainly - John 3:16, Gal 3:26, etc.
Confession - Rom 10:17
Repentence - Acts 2:38
Grace - Eph 2:8f
Endurance - Mt 24:13
God's Mercy - Tit 3:5
Love of the truth - 2 Thess 2:10
The gospel - 1 Cor 15:1ff
Perseverance - Lk 21:19
etc. etc., and of course, baptism I Peter 3:21, Acts 2:38
"The SUM of Thy Word is truth..." Ps 119:160