This is an often stated criticism of modern Lego designs, but I wonder if anyone has tried to test this empirically?

E.g. if you gave a group of kids a "classic" set and another a themed set, with no further instructions, would the first group produce more "creative" designs?

I think the critics of the branded sets undervalue the Piagetian concept of scaffolding, basically that having the Harry Potter superstructure allows kids to riff on a variety of concepts that actually may be more "creative" than the random geometric blocks.

E.g. "What if we built a jail around Voldermort instead of killing him" seems like an equally valuable expression of creativity as "I made a vaguely car-shaped thing, but it has six wheels instead of four and has those little lever bricks instead of a steering wheel."