There is a form of historiography described as Great Man theory. As the name suggests, it sees history most fundamentally as the result of great men doing great deeds. Although largely and rightly discredited, it still maintains a subterranean influence upon historical thinking. Perhaps the most demonstrable instance in which it emerges in the study of early Christianity is in the role often attributed to Marcion.
Dating back at least as far as Harnack, there has been a sector of early Christian studies that sees Marcion as a major causal factor in the development of such things as the canon, doctrine, the episcopacy, church law, etc. He crafted a biblical canon; therefore, the church responded with one of its own. The church found his beliefs objectionable, and thus set out to clarify their own at a level previously unprecedented and to develop an ecclesiastical structure (the episcopacy) that could enforce these as normative and the church laws necessary to sustain that structure. Such arguments have been, and continue to be, made regarding Marcion's supposedly crucial role in the development of Christianity. Today, there is a small but vocal minority that argues that Marcion's Gospel, which the church fathers report to be an edited version of Luke's, was on the contrary a source for Luke's and perhaps one or more of the other Synoptic gospels.
Many such narratives are, if not demonstrably false, somewhere between possible at best and highly dubious. For instance, in order to judge that Marcion's Gospel was a source for one or more of our canonical gospels one has to judge that every single possible pre-Marcionite attestation to these gospels does not constitute such an attestation; the statistical probability of this being the case seems quite low, and that does not begin to cover the problem of parsimony provoked when we potentially multiply entities that look virtually indistinguishable from but in fact are not our extant gospels. Or, take the example of canonical development. Yes, it does seem to be the case that Marcion's list of what constitutes Christian scripture is the earliest one extant among our evidence. It does not necessarily follow that he originated the idea of a canon of Christian scriptures. That is a hypothesis, and it could be true, but the argument from silence does not seem adequate to establish that it is. And that's really all that the "It's the earliest extant, therefore it was the first to exist" hypothesis has going for it. Nor does it follow that his canonical list was causal for subsequent lists; post hoc ergo propter hoc is fallacious for a reason. It is in fact a very naive empiricism that assumes that because some comes first in an extant sequence it is both the first moment in that sequence and causal for what follows.
More fundamentally however, these sorts of narratives tend to suffer from the same flaw that Herbert Spencer identified in Great Man theory 150 years ago: contrary to Great Man theory and its obsession with the genius and autonomy of the gifted individual, "great men" are the products of history, and are only able to achieve what they achieve because of the situations from which they emerged and to which they are responding. Their greatness lies not in their individual genius and their creations ex nihilo, but rather in how they work with the resources available to them to respond to the problems of their day. No genealogical investigation into the development of notions of canon or the establishment of church hierarchy for the Great Man theorist: no, these are but the response to the Great Man. Marcion the Great, after whose titanic stride across the pages of history Christianity was never again the same, emerges almost as Melchizedek, without genealogy.
It should be noted that Great Man theory is not identical to discussing the operations of named individuals. Historians often can and do state that this or that woman or man performed this or that operation at this or that time. It is a perfectly legitimate historical question to ask "Did Peter contribute to the traditions found in Mark's Gospel, and if so in what fashion?" What distinguishes such questioning from Great Man historiography is that it recognizes Peter not as an autonomous genius nor a novum that serves as a functional deus ex machina, but rather his operations as one set of effects situated among many in a larger constellation of historical movement. This is precisely the opposite of the Melchizedek narrative, for Peter not only has genealogy but now is integrated fully into one. Such genealogy is precisely what I find missing in much (although certainly not all) of the invocation of Marcion in early Christian studies.