No offense, I don't know where you did your research but I don't see anywhere on Marvel's landing page where it makes clear its main flow is PSD -> storyboard. In my opinion, Marvel's landing page makes it very clear that workflow is paper -> photo -> storyboard just like Popapp, but also supports importing a PSD image (which doesn't seem like a groundbreaking differentiation). Granted, the founder explained the difference somewhere above but they're still "improvements", they fundamentally do the same thing.