Thanks for creating and sharing the video. I am, of course, in agreement... though if I may offer three comments that could help tie some of the content together.
That the Matthean sermon is a literary creation could be reinforced using a wide-lens analysis of the gospel's literary structure... you touch on, for example, the community and mission discourses, which are the second and fourth of five such sayings complexes that Matthew either inserts whole cloth (the aforementioned sermon) or inflates in parallel to a terse Markan version (the remaining four discourses), bringing them to a total of five in his particular presentation of Jesus as a new Moses and interpreter of the Torah. Your argument could be strengthened by drawing specific notice to these five blocks as part of the gospel's literary artistry.
In response to the idea that Matthew's "Sermon on the Mount" and Luke's "Sermon on the Plain" constitute two different sermons separated in time, it could be argued that they are inserted at the same point chronologically in the Markan framework and thus constitute different versions of the same ostensible sermon. While it is common for proponents of the two-document hypothesis to claim such alignments of so-called Q material never occurs, it actually does on several occasions... this being one of them. The three gospels synchronize with Jesus going up on the mountain and some disciples gathering around him:
When he saw the crowds, he went up the mountain; and after he sat down, his disciples came to him. (Matt 5:1)
He went up the mountain and called to him those whom he wanted, and they came to him. (Mark 3:13)
Now during those days he went out to the mountain to pray; and he spent the night in prayer to God. And when day came, he called his disciples... (Luke 6:12-13a)
Anxious to get to his first block of sayings, Matthew postpones the selection of twelve apostles that occurs on this mountain in Mark and Luke to later in his narrative (would Winger suggest Jesus did this twice?), but otherwise the sermons are aligned... Luke simply has Jesus come down from the mountain with his newly-appointed apostles to meet the large crowd that Matthew reported immediately prior to Jesus' ascent (4:25), heal some of them and then launch into the sermon. Someone such as Winger would have to argue Jesus delivered these sermons back-to-back to the same audience (Matthew from the mountaintop, Luke on equal footing), which attempted harmonization strains credulity.
A third point concerns Luke's own literary arrangement of the material. While I can appreciate that the video was focused on Matthew's version of the sermon as a literary creation, showing how Luke's version is also stylized would help reinforce the overall approach you present of how early Christian writers interacted with the sayings of Jesus when composing their biographies. Luke's version is, as you note, significantly shorter... it happens to be arranged, however, in three distinct blocks of material: (1) 6:20-26 presents the introductory blessings (balanced by woes lacking in Matthew), (2) 6:27-38 constitutes Jesus' ethical demands on his followers culminating with the illustration about the good measure, at which point the narrator intrudes with a note that Jesus tells them a parable (6:39a), followed by (3) several other such illustrations (the blind guide, the disciple and his teacher, the log in the eye, the tree that is known by its fruit, treasures of the heart and the two houses) through to the end of the sermon (6:39b-49). Matthew's version is a hodge-podge of sayings that Luke can be seen polishing off... literary artistry at work, not the raw recording of a sermon.
Kind regards,
Jonathan
