Part of what makes this so popcorn-worthy is that, if the game releases and Skillup is vindicated (Jason Shrier giving tentative confirmation) then it'll prove something we've long suspected - the reviewers across the board make a habit of playing through a game on the easiest difficulty to bumrush the game and get a story out.
Morty does 100% achievement runs. If there is an achievement for beating the game on hard, then he has done so.
But yes, I do suspect, and even expect, that rushing to finish the game involves playing it on the easiest difficulty. How would it not?
Years ago there was some review commenting on actual game mechanics, like invisible barriers or whatever, that only work that way on easy. And then the reviewer complained about the bad ending, but the game only ends that way on easy mode. On every other mode, you get a different, cooler ending. When the developer said as much on Twitter, they redacted the review text, but kept the score low, despite deleting the given reasons for why it is low. A screenshot of this review was reposted often during Gamer Gate, someone might have it.