Is there such a thing as an unimaginative child (or a practical one, for that matter)? As a child I seem to recall that all my friends and classmates were imaginative and creative, and my child and his friends are just the same in that way. Lego is universally popular, as is playing "pretend", and so on.
Obviously these traits are present in children to different degrees, but I think the point of this book is to emphasize that the lack of imagination and creativity in adults and its replacement by banality and commercialism is the product of socialization and choice.
> Imagine the story was written in the same manner, but in praise of physical coordination/agility instead
We'd probably be offended if, in that case, the uncoordinated people were drawn as obese (although the same effect could be achieved by simply displaying them as immobile). What's interesting, though, is that the book actually could be written that way. Children are far more active than adults and, because physical coordination and agility can be improved through practice, are often faster and more nimble than adults (I'm speaking anecdotally here, but if you visit a playground and watch a kid evade their parent and the point is made.)
Just as imagination and creativity are often lost or suppressed on the journey to adulthood, many people also shed their love of physical activity, with unfortunate results.
Perhaps the point, ultimately, is that there's lots we can learn from children, and much that is in them innately that we can help nourish.
I am quite sure the educational environment in the 19th century was _way_ less keen on letting imagination run wild than it is now (e.g. montessori's work was disruptive but looks "normal" nowadays), but we have Peter Pan and the Neverending Story only in the 20th.
I think you've conjured the word 'ordinary' out of the air and made up an example that supports your made up word. This book like all children's books is a way for parents to put something into their child's mind. In this case it is a book that tells children and reminds parents that dreaming is great.
The 'ordinary' people you feel are getting portrayed so badly aren't 'unable' to dream or disadvantaged in any way they just don't dream of very impressive things.