Lately I've been writing about what I think is the direct trajectory of Synoptic interrelations by way of Mark > Matthew > [Marcion >] Luke. That is, that Q isn't necessary to explain the similarities between Matt and Luke; that Luke used Matt as a source (or used a source that used Matt as a source – some heretical Synoptic gospel a la Marcion) and not Q.
I posted an image of the relationship between the Synoptic gospels in one of those posts. There's one part that gives me pause about the whole hypothesis though: The 1% of overlap between Mark and Luke that is not shared in Matt. If what I had originally proposed was true, then Luke could have reconstructed Mark completely using only Matthew, but this is obviously incorrect. This 1% is a single pericope, the one where Jesus exorcises the demon from the synagogue in Capernaum. In Mark, it is Jesus' first demonstration of his
21 They went to Capernaum, and when the Sabbath came, Jesus went into the synagogue and began to teach.
22 The people were amazed at his teaching, because he taught them as one who had authority, not as the teachers of the law.
23 Just then a man in their synagogue who was possessed by an evil spirit cried out,
24 “What do you want with us, Jesus of Nazareth? Have you come to destroy us? I know who you are—the Holy One of God!”
25 “Be quiet!” said Jesus sternly. “Come out of him!”
26 The evil spirit shook the man violently and came out of him with a shriek.
27 The people were all so amazed that they asked each other, “What is this? A new teaching—and with authority! He even gives orders to evil spirits and they obey him.”
28 News about him spread quickly over the whole region of Galilee.
Similarly in Luke 4.31-37:
31 Then he went down to Capernaum, a town in Galilee, and on the Sabbath began to teach the people.
32 They were amazed at his teaching, because his message had authority.
33 In the synagogue there was a man possessed by a demon, an evil spirit. He cried out at the top of his voice,
34 “Let us alone! What do you want with us, Jesus of Nazareth? Have you come to destroy us? I know who you are—the Holy One of God!”
35 “Be quiet!” Jesus said sternly. “Come out of him!” Then the demon threw the man down before them all and came out without injuring him.
36 All the people were amazed and said to each other, “What is this teaching? With authority and power he gives orders to evil spirits and they come out!”
37 And the news about him spread throughout the surrounding area.
So yeah. Luke has to be using Mark here since the wording is near identical. Especially the words that Jesus and the demon(s) speak; the words spoken in Mk 1.24-25 are nearly equivalent to the words spoken in Lk 4.34-35. The only difference is the word λεγων (saying) in Mark is replaced with εα (leave us alone or ha!) in Luke. What's also interesting is that Marcion's gospel also has the same exact spoken words as Luke, except that Marcion leaves out the vocative Nazarene (Ναζαρηνε) since it didn't make sense in Marcion's narrative that Jesus would be referred to as being from Nazareth (by this time, Nazarene had probably already lost its original meaning and was probably equated to one being from Nazareth) as soon as he had descended from the Father straight into Capernaum.
So it might be that Luke is indeed using Mark as a source as well as Matt and Little Marc.
This, as J. Tyson points out in Marcion and Luke-Acts, makes sense of the opening of Luke: That “many” (πολλοι) had composed narratives about the life of Jesus and he set out to write a better account. I can't see how only Mark and Q could be considered “many”. But Mark, Matt, Marcion, (and possibly a source that Marcion might have used; some sort of proto-Luke that looked a lot like Mark) would most certainly fit the logic of “many”. I also can't see how “many” could apply earlier than the existence of any supposed Christian heresies – prior to the 2nd century.