I would probably start by saying Jesus said water AND spirit, not water OR spirit, in John 3.
I am not a fan of that word necessary. The Catechism gives a good definition, especially the last sentence…
CCC 1257 The Lord himself affirms that Baptism is necessary for salvation. He also commands his disciples to proclaim the Gospel to all nations and to baptize them. Baptism is necessary for salvation for those to whom the Gospel has been proclaimed and who have had the possibility of asking for this sacrament. The Church does not know of any means other than Baptism that assures entry into eternal beatitude; this is why she takes care not to neglect the mission she has received from the Lord to see that all who can be baptized are “reborn of water and the Spirit.” God has bound salvation to the sacrament of Baptism, but he himself is not bound by his sacraments.
The importance of Baptism is all over the Bible, especially John 3. I would be curious what reasoning he has come up with, to conclude that it is not important.
My all time favorite verse to date was the guy that said Mark 16:16 proves Baptism isn’t necessary.
Mark 16:16 He who believes and is baptized will be saved; but he who does not believe will be condemned.
His reasoning was since Jesus didn’t repeat the word baptized in the second half of the sentence that means he didn’t really mean it in the first half. Interesting?
Hope this helps,