Bart Ehrman's irrational faith (in Q)

If you've been following this blog for a while you might remember the '$1,000 Challenge to Bart Ehrman'. The focus of this challenge was whether Bart Ehrman had a specific reason for thinking that Matthew did not copy Luke. At that time Bart declared himself "completely convinced" by an argument offered by Mark Goodacre - even though this was an argument that didn't address the question of whether Matthew used Luke. 

A few days ago I tried asking a related question in an AMA with Bart Ehrman:

Robert Derrenbacker recently wrote:

"[I]f, for the sake of argument, one were to dispense with Q and maintain Markan priority, Matthew's use of Luke (as advanced by the supporters of the MPH) actually makes the best sense of the material in a Mark-without-Q scenario."[1]

Do you agree that Matthew using Luke (with Markan priority) is a more likely solution to the Synoptic Problem than Luke using Matthew?

Bart's full answer can be found in the clip posted above. The original context is Reddit/AcademicBiblical/BartEhrman-MatthewAMA

The arresting thing about this answer is that (after explaining the Q Theory) Bart offers a reason why he thinks Luke did not use Matthew. What he doesn't go on to do is offer a comparable reason why Matthew could not have used Luke. This might be because the mechanics of Matthew's use of Luke are closely parallel to the mechanics of Matthew's use of Q (which Bart evidently doesn't find problematic).

Without a specific reason why Matthew could not have used Luke, Bart's belief in Q has no rational basis. His concluding argument, "nobody thinks that", is not just bad logic it is also demonstrably untrue. 

See also: Swinging big and swinging blind: Bart's extra gamble

[1] Robert Derrenbacker Jr., '"Unfinished" Mark "Replaced" by Matthew and Luke? Some Recent Studies and their Implications for the Synoptic Problem', in The Synoptic Problem 2022: Proceedings of the Loyola University Conference, Olegs Andrejevs, Simon J Joseph, Edmondo Lupieri, Joseph Verheyden (eds) (BiTS 44, Peeters, 2023) page 193.