(The "Synoptic Problem" is one part of the problem of multiple gospels. It is quite independent of the relationship of John to the other gospels.)
Mark's gospel has about 660 verses, all but twenty or so of which reappear in Matthew and Luke. Matthew reproduces almost 600 of Mark's verses and Luke about 300.
Where the synoptic gospels agree on the ordering of the material all three agree. When Matthew and Luke diverge from the ordering of Mark they also disagree with each other.
The koine or common New Testament Greek of Matthew and Luke is much better written and smoother than that of Mark.
These facts are taken to indicate that Mark's gospel was the earliest written.
The Structure of Mark's Gospel.
The Introduction; (Mark
1:1-13)
The Ministry in and around Galilee; (Mark 1:14 to 9:50)
The Journey to Jerusalem; Mark
10.
Jesus in Jerusalem; (Mark 11:1
to 6:8)
The Resurrection; (Mark
16:9-20)
This structure is repeated in the other synoptic gospels but is not followed in John.
(1) The "Messianic Secret." (Hayes, 339-340)
(Mark
1:44, 3:12, 5:43, 7:36, 8:27-30) disciples, (Mark 9:2-9) The
Transfiguration)
(2) The Misunderstanding of the Message. (Hayes, 339)
(Mark 6:52, 9:9-10)
In fact it is said that Jesus' teaching in parables was to hinder peoples'
understanding.
Particularly the disciples and Jesus' family are shown as blind to his meaning, and as
finally deserting him, (Mark14:50)
and denying him, (Mark
14:66-72). Following the will of God is explicitly said to be more important than
blood relationship to Jesus,
(3) The Hostility of the Jews. (Hayes, 340)
(Mark
2:6, 3:6, 6:4, 8:11, 10:2, 12:13, 14:1, 55, 15:11, 31-32),
(4) The Kingdom of God. (Hayes, 345-350)
Mark
1:14-15, 2:18-22, 3:22-27, 4:11, 26-29, 9:1, 42-48, 10:15, 23-25
Did Jesus in Mark's Gospel preach the Kingdom as present, as potential, or as yet to come?