In the introduction to Dieter T. Roth's article, "Marcion’s Gospel and Luke: The History of Research in Current Debate" (JBL 127, no. 3, 2008, pp 513–527), he says:
The issue of the relationship between Luke and Marcion’s Gospel has been revived recently in several discussions of Marcion and Luke-Acts.1
Although this renewed interest is to be welcomed because of the importance of the question for the study of the canon, the fourfold Gospel collection, the Synoptic Problem, and text-critical issues pertaining to the Gospels in the second century, it is curious that numerous, including the most recent, summaries of the veritable flurry of work in Germany in the 1840s and 1850s have been marred by inaccuracies.
These erroneous views have then, at times, been employed to develop a connection to and draw support from the purported consensus of German scholarship by the mid-1850s on the relationship between Luke and Marcion’s Gospel, when no such consensus actually existed.
Thus, the incorrect impression has arisen that recent advocates of the position that Luke was the product of a significant redactional revision after the time of Marcion are renewing a supposed consensus that resulted from the intense discussion of the issue in Germany 150 years ago.
In the light of this besetting problem, the purpose of this article is to revisit the scholarly debates concerning Marcion’s Gospel in the mid-nineteenth century in order both to  provide an accurate presentation of the history of scholarship in this period and to address the claims found in recent discussions.
1) Whenever “Luke” is used in this article without qualification it refers to the text of canonical Luke as we know it. Recent discussions of the relationship between Marcion’s Gospel and Luke include
• Andrew Gregory, The Reception of Luke and Acts in the Period before Irenaeus (WUNT 2/169; Tübingen: Mohr Siebeck, (2003), 173–210;
• Matthias Klinghardt, “‘Gesetz’ bei Markion und Lukas,” in Das Gesetz im frühen Judentum und im Neuen Testament: Festschrift für Christoph Burchard zum 75. Geburtstag (ed. Dieter Sänger and Matthias Konradt; NTOA 57; Göttingen: Vandenhoeck & Ruprecht, 2006), 99–128; idem, “Markion vs. Lukas: Plädoyer für die Wiederaufnahme eines alten Falles,” NTS 52 (2006): 484–513; idem, “The Marcionite Gospel and the Synoptic Problem: A New Suggestion,” NovT 50 (2008): 1–27;
• and Joseph B. Tyson, Marcion and Luke-Acts: A Defining Struggle (Columbia: University of South Carolina Press, 2006).
I reformatted the text to make the points stick out, and underlined what I take to be his overarching theme.
He is not at all impressed by the accuracy of modern summaries of German language Marcion research of the 1840s-50s, and one gets the impression that he thinks the modern scholars have been dishonest in their summaries. I also get the impression that he felt that the mid-19th century researchers were getting ahead of themselves.
He then proceeds to show the reader what these mid-19th century scholars "really" said, demonstrating to his satisfaction that there was no consensus then that Marcion's Evangelion served as the basis for canonical Luke.
There is, I think, a tiny bit of apologetic defensiveness by using words like "curious," "inaccuracies," "flurry," "purported" and "supposed." However, he does give a very thorough survey of mid 19th to early 20th century German scholarship, hopefully relatively free of those "curious inaccuracies" he complains about (dream on!).
The relationship to the OP is that if modern scholars can allow their wish to make Marcion's Evangelicon the basis of the NT Luke skew their summary of previous research, cannot we also assume that modern scholars have done so when explaining the development of Christ theology as myth?
To be fair, this is true of scholarship of all peoples in all times, a timeless truth, that researchers always interpret the evidence in conjunction with the spirit of their age/time/place, as they have experienced it. There is no "truth" that is not also subject to change and development over time, as opinions and biases develop over time. Boo hoo!
But what fun it is to read, and pick apart, the works of predecessors. Whoo-hoo!!