The prominence which Jesus gives to John the Baptist requires specific explanation. After all, he is put on a level with, or perhaps even above, Moses, Abraham, Jacob and all the other greats; yet by the usual understanding, that status seems hard to justify.
What exactly, did John the Baptist do that was so important and can stand comparison, indeed excel, the remarkable achievements of the ancient Hebrew prophets?
It would be expected that we would be told exactly what that achievement was, and indeed we are. We are told what John did, and its effect - he was The Baptist, and he baptised Jesus, and this was the act that put him above all other prophets.
As we are told John was supremely important, the baptism of Jesus by John must itself have been supremely important. Well, we are told in the Fourth Gospel that the (divine) Spirit came and rested and stayed upon Jesus. Since we were not told anything about Jesus's earlier life in the Fourth Gospel; implicitly, this marks the exact moment when Jesus became what he finally was, and without this he would not have been who he was.
In the Fourth Gospel, there is no 'origins' Nativity story, no genealogy of Jesus, no information concerning Jesus's childhood (nothing about Jesus being related to John the Baptist). John's Baptism is apparently the sole and sufficient explanation of Jesus becoming fully the Son of God.
Of course Jesus was already the Lamb of God, even before he was baptised, and was recognised as such... by John the Baptist.
Therefore, the Fourth Gospel is telling us that it was John the Baptist who first recognised that Jesus was the Messiah, and on baptising him was aware of the Spirit descending upon him and staying upon him.
We tend to assume that none of this was essential to the work of Jesus; but we are probably wrong to do this. At least in the Bible, God does things by Men. Perhaps if one man fails, then God may find another - but decisions and events have permanent significance.
It seems that the weight of the divine plan of salvation rested upon the shoulders of John the Baptist; and that he was needed as the specific person who was worthy and able, to recognise and baptise Jesus, in the decisive event which began the ministry of Jesus.
Since the author of the Fourth Gospel gives no other 'reason' for Jesus's status; the recognition and Baptism by John may count as the single most important event in the mortal life of Jesus.
If that is so; the prominence of John the Baptist in the Fourth and Synoptic Gospels is easily understandable.