Obviously, Jesus was excluding Himself from that statement. I really doubt that anyone would argue otherwise, certainly not John the Baptist.
To exclude Mary from that statement is a heroic assumption. In a sense, Mary is part of the prophetic line as the "Virgin with Child." Certainly, Mary's Song in response to Elizabeth's proclamation contained prophetic elements. It would be far more logical to include Mary with the prophets than it would be to exclude her.
he goes on to say that the least in the kingdom of heaven are greater than John
The fact that Jesus said that John was less than the least in heaven is irrelevant here. Both John and Mary were on earth.
("the Prophets and the Law prophesied until John").
This expression really shows what honor that Jesus was bestowing on John. Many people identified Jesus as the long-awaited Messiah including Mary, Elizabeth, Anna, Simeon, etc. but the proclamation that really mattered was John's. John was special among prophets because he was given the authority to say "That's Him." Obviously, both John and Mary had important roles but contrary to Marian Dogma, it seems Scripture assigned John a higher role. Do not forget Luke 11:27-28 when Jesus Himself redirected the focus of the woman who tried to heap praise on Mary.
Selah ... here is wisdom.
[Reply:}The fact that Jesus said that John was less than the least in heaven is irrelevant here. Both John and Mary were on earth.
But Jesus was also on earth at the time; and He said "kingdom of heaven", not just "heaven". This is important, for He also said, "the kingdom of God is within you" (Luke 17:21). I take what he is saying to refer to the giving of the Holy Spirit to those in the kingdom of heaven, following the distinction between John's baptism with water and the baptism with the Holy Spirit that he and the NT writers draw in a number of passages (Matthew 3:11, John 1:24-27 and 3:3-8, Acts 19:3-6, etc.). Mary was "overshadowed" by the Holy Spirit (Luke 1:35), and the sound of her voice fills John's mother with the Holy Spirit and makes John leap for joy (Luke 1:41). Regarding Luke 11:28, that can be translated as "Blessed *indeed* are those who hear the word of God and obey it," which would be emphasizing that Mary is blessed because she heard the word of God and obeyed it ("Be it done unto me according to your word": Luke 1:38), not merely because she is physically related to Jesus; that is how I take that passage.