Is Doubting Thomas doubtful?

Moreover, with Judas now dead, there were eleven main disciples. Thus Luke 24:33 can speak of Jesus's first appearance to a group of his male disciples as including "the eleven and those with them." However, John 20:19-24 tells us Thomas was absent during that event. Thus, only ten of the main disciples would have been present. Accordingly, either Luke conflated the first and second appearances to the male disciples, or John crafted the second appearance in order to rebuke those who, like Thomas, heard about Jesus's resurrection and failed to believe it. M. Licona, Why are There Differences in the Gospels? (Oxford U 2016), 177-78.

A few observations:

i) It's not my primary objective to offer my own harmonization. But I'll make two brief observations. I think Luke and John were written about 30 years after the event. By that point I think it would be natural for "the Eleven" to be a stereotypical descriptor. Because the Gospels (and Acts) are written from a retrospective viewpoint, it's not unexpected if they'd use terms that reflect later usage, just like a historian might refer to a particular state as Arkansas even though it was technically Indian Territory at the time the historian is referring to. Historians sometimes employ conventional anachronisms to make historical referents recognizable to modern readers. I suspect that by the time of writing, "the Eleven" was a traditional designation rather than a count noun. 

I'd add that, assuming traditional authorship, John has firsthand knowledge of the event whereas Luke has secondhand knowledge of the event. Therefore, it's not surprising if John's account of this particular incident is more detailed, whereas Luke's is more sketchy. An outline and a plot are both compatible. 

ii) I don't object to the category of redaction in reference to the Gospels, but it's overused. There's a common assumption that redaction is theologically motivated. But I think redaction is typically more mundane: to touch up the language, to free up space for independent material, to forestall a misunderstanding on the part of the reader.

iii) Let's talk a bit about genre. Suppose a director makes a movie about a past event, like the Civil War. The movie might be classified as historical fiction. We expect the director to exercise artistic license. 

Even in that respect, there's a difference between artistic license and historical revisionism. For instance, Ridley Scott was criticized for airbrushing Islam and minimizing Medieval Christianity in Kingdom of Heaven. That wasn't a case of taking artistic liberties to improve the dramatic values of the story. Rather, that was filtering the past through the political and secularizing sensibilities of a British director, c. 2005. Even in a fictional or quasi-fictional genre (historical fiction), where we make allowance for artistic license, that doesn't justify an ideological misrepresentation of the past. 

iv) Compare a movie about the Civil War to an account of the Civil War by an academic historian. It would be unethical for him to "craft" an incident that never happened. That's because we're reading the book for information about what really happened.

By the same token, Christians have always read the Gospels for information about the life of Christ. The Gospels are the backbone of the Christian faith. 

v) Notice, too, the openness to classifying a reported Resurrection appearance as a fabrication. But if that's a fabrication, what about the other Resurrection appearances in John? And if the Johannine narrator concocts imaginary accounts of the Resurrection, what about the Synoptics? 

vi) Moreover, the purpose of recording this particular anecdote is to attest the reality and physicality of the Resurrection. Jesus is not a ghost! This wasn't a vision of Jesus. Rather, God bodily restored him to life. To suggest this account may well be pious fiction is especially ironic for a Christian apologist who makes the Resurrection the centerpiece of his apologetic.