How Could the Marcionites Have Been 'Literalists' If They Believed Jesus Floated Down from Heaven at the Beginning of the Gospel?

You know how scholars often work in 'academic sound bytes' - i.e. they fail to look at the 'big picture' when they develop their pronouncements.  Bart Ehrman made it explicit in his 2005 book Lost Christianities when he claimed 'Marcion was a literalist.' (p 111)  But how exactly is that possible?  We are supposed to believe that they literally believed that the gospel writer Paul - a man who never saw any of the events described in his gospel, 'literally' developed the account of a supernatural god-man appearing on earth, passing through crowds but somehow managing to get nailed to the Cross.  How is that possible?  And what exactly is the evidence for this claim?

The fact that they were sticklers for the exacting wording of passages shared with other gospels does not prove that they were 'literalists.'  The fact that von Harnack famously claimed "[t]here was no theologian in the early church who rejected allegorical interpretation as consistently as did he" does not prove anything either way.  We must demand that those who claim that Marcion denied allegory as such should bring forward their evidence. 

The most common tactic to bolster this argument is to note that the Marcionites supposedly did not allow for allegory and so 'must have' also denied it for the gospel.  But this is a stupid line of reasoning.  If, as is often suggested, the Marcionites 'opposed' Jewish scripture it would not be surprising that one does not allow one's opponents refuge in allegory.

J. G. Gager suggested that Marcion's rejection of allegorical interpretation of the Old Testament is the result of a philosophical education. As known, Plato, Eratosthenes, Aristarchus, and Epicurus came out against allegory. But where exactly is the evidence that Marcion 'came out against allegory'? I still don't find that anywhere in these sources.

The only two sane views I can find are Dungan, who contends that Marcion's use of antithetical statements does not necessarily speak to his rejection of allegory as a means for ameliorating and Schmid (not surprisingly) who follows this assessment with examples of Marcion's employment of allegory (Marcion, 255—260).

Half the work in scholarship is to clear away the nonsense cultivated by predecessors.