Can't the floor plan of a gable roof house work in a full upper floor?
No, that inevitably creates an excess of space: suddenly, you have gained fully usable space on areas that with a gable roof would only have been good for vacuuming, making the rooms effectively larger. One could react by making the rooms correspondingly smaller in floor area: a bit on the left, a bit on the right, except that you don’t want anything in these newly freed-up spots. And ironically, in the concrete example, this would mean that the pantry displaced on the ground floor would suddenly find a place in the upper floor. But what would you want to do with it there?
Therefore, it is wiser to understand a two-story house as a different category than a one-and-a-half-story house and to devise a corresponding different mass distribution rather than trying to quasi "transgenically" transfer a floor plan onto another house type.
Just imagine the two floors in cross-section (so the full floor as a rectangle, and the gable roof floor without knee walls as a triangle): the rectangle has twice the "area" with the same base and height. Accordingly, the floor area of a full-floor room "weighs" as more space than the gable roof counterpart.
You have to rebalance the total area distribution between ground floor and upper/attic floor; otherwise, a person with shoe size 42 suddenly has rooms of shoe size 46 under their feet.
In terms of this far-fetched comparison, you have basically put boots instead of sandals on the house; that is indeed more than just a visual difference.