How would you explain the verbal overlap between the Synoptic Gospels?

I would explain the verbal overlap between the Synoptic Gospels as follows: Mark composed his Gospel first, and Matthew and Luke are inspired revisions of or reflections upon Mark’s composition. That Matthew and Luke incorporate so much of Mark’s presentation is itself an affirmation of Mark’s authenticity rather than an undermining of it. Despite the inclusion of differing materials and variations in wording, the Jesus they present is congruent with Jesus as He is presented in Mark. This view, more formally known as the 4-Source Hypothesis, makes the best sense of the available data and is the dominant explanation for good reason.

According to one variation of this view, the Gospel of Mark originated as a collection of Peter’s remembrances of Jesus which were recorded by Mark (Peter’s interpreter). This tradition finds early support in Papias. Mark’s Gospel was quickly embraced by the early Church and was accepted as authoritative because it contained apostolic tradition. It would have made little sense for Matthew and Luke to start from scratch in their accounts of the life and works of Jesus. For this reason, Matthew and Luke incorporated the vast majority of Mark’s materials because they agreed that Peter’s recollections accurately reflected both who Jesus was and what He did.

Nevertheless, Matthew and Luke had the freedom to nuance details and reorder the sequence of events in whatever manner best fit the intended aims of their Gospels, since Mark made not attempt at a chronological presentation. They also shortened some sections of Mark and expanded others, as well as adding their own material.

The 4-Source Hypothesis is more plausible to me than the theory that Matthew, Mark, and Luke just happened to have precise verbal overlap on many occasions and that they arrived at that overlap in complete ignorance of one another. Luke opens his Gospel by acknowledging that “many have undertaken to draw up an account of the things that have been fulfilled among us” and that he “carefully investigated everything from the beginning” (Luke 1:1-3). With this acknowledgement it should not surprise us to find he embraced Mark. Additionally, though Matthew was himself an eyewitness of many of the events recorded in his Gospel, why should we object against his utilizing Mark’s record? There is no known 1st Century Handbook for Gospel Writers which prohibits making use of another’s work. The fact is that 85% of Mark shows up in Luke and 95% of Mark shows up in Matthew. Moreover, we sometimes find that where there is verbal agreement there is even agreement in the chronology of the presentation in two or even all three of the Synoptics, further suggesting that Matthew and Luke were both dependant upon Mark.

For example, in the case of the common tradition preserved in Mark 2:1-12 // Matthew 9:1-8 // and Luke 5:17-26, Luke uses 35% of Mark and Matthew uses 33% of Mark. It’s evident that there is some form of dependence occurring here. Matthew seems to have taken up Mark’s tradition and conflated it, excising some of the details while retaining other sections word for word. Luke, on the other hand, retains more of Mark’s details and even adds further elaborations (i.e., in 5:26 where he adds that the people were not only amazed and glorifying God but were also “filled by fear”). Were there only a handful of rare occasions when verbal overlap occurred between Mark and the other two Synoptics, perhaps we could argue it was the mere result of chance, or that all three Gospel writers had a general familiarity with preceding oral traditions. But the number of instances where these overlaps occur makes far more plausible that Matthew and Luke were familiar with Mark’s Gospel and were consciously embracing some components of his presentation.

So, what are your thoughts on this? Do you think this is reasonable or unreasonable, and are there any implications to this if it's accurate? Does this in any way impact our definition of inerrancy or our understanding of the inspiration of Scripture?