Isn’t the disciples’ doubt just a literary device to preempt skeptics, rather than honest reporting?

It could be, but notice what the device costs. The Gospels portray the founding leaders of the church as slow, frightened, and unbelieving. A movement inventing stories to shore up its leaders’ authority does not usually write Peter denying Jesus three times or the apostles dismissing the women’s report as nonsense. The criterion of embarrassment applies here: details that make your own side look bad are more likely to be remembered than invented.