The argument from Luke's lack of Matthew's modifications of Mark seems to be refuted by a simple glance at the Synopsis.
This material is of course familiar to scholars using the argument about Luke's lack of Matthew's additions to Mark, but the force of this evidence, and the fact that it contradicts one of the standard arguments is not felt. The primary reason for this [21] is that examples of this kind are placed in the special category of "Mark-Q overlap", those passages occurring in all three Synoptics in which Mark is not clearly the middle term, which blur the usually more straightforward distinction between "triple tradition" and "double tradition". The fallacy at the base of this argument for Q is that where Luke (on the assumption of Marcan Priority without Q) prefers the Matthean version of a pericope shared with Mark, this automatically goes into the category "Mark-Q overlap". And where Luke prefers the Marcan version of a pericope shared with Matthew, this is held to demonstrate his lack of knowledge of the Matthean versions of Marcan pericopae