We have to look at Matt 11:7-9 for context.
As John’s disciples were leaving, Jesus began to speak to the crowd about John: “What did you go out into the wilderness to see? A reed swayed by the wind? (Have to love Jesus's wit) 8 If not, what did you go out to see? A man dressed in fine clothes? No, those who wear fine clothes are in kings’ palaces. 9 Then what did you go out to see? A prophet? Yes, I tell you, and more than a prophet.
Jesus knew their intent. They came to see a ''great man''. They saw a man in rags living off insects. Jesus made it crystal clear to all in verse 11, that they were in the presence of the greatest man ever to live on earth.
The second part of verse 11, ''even the least in the kingdom was greater than John'' is to clarify the importance / relevance of the message John is preaching.
I will try better explain: People come to see a great man, they don't. Jesus says he is greatest man ever to live. Jesus then says the person that is baptized is even greater. It should be obvious that the contrast of 'greater' is, John 'as he is'. A great man on earth. Whoever is baptized is grafted into God's family. Being a child of God, inheriting heaven, is greater then being a great man on earth. This verse does not say John has not inherited heaven. It is very important to grasp the context of statements in these verses. John was born of a mother and father. A person baptized / Christian is now born of God.
John 5:1 Everyone who believes that Jesus is the Christ is born of God.