Personally and IMHO I don't lump Frank Lloyd Wright in with the Chicago School of Sullivan and Mies. I think the latter were influenced by a rather mechanistic, "escape from nature" view. The idea that skyscrapers were born in flat Chicago should tell us enough about that.
I really love Mies for his advancements in spartan architecture and the beautiful purity of his work: he advanced Sullivan's "form follows function" incredibly. His Barcelona Chair is a marvel of modern design, sleek and streamlined of "nonfunctionality."
(Of course, then he went and bolted functionless i-beams on the Seagrams Bldg and 845 Michigan Ave...)
Wright on the other hand was a whole nuther creature. I believe it was his contribution to architecture you are referencing, namely his use of nature not only as metaphor but as archetype.
His prairie houses' "horizontal linearity" evoke the far horizon of the plains, but he went much farther in studying nature: some of his buildings, in how they copy "natural principles," also are marvels of engineering. (Not Fallingwater!)
For example, his adaption of tree trunks into a "core" for skyscrapers is an idea that has so permeated modern design, offhand I can think only of the World Trade Center towers as examples of modern skyscrapers that depend(ed) on load-bearing perimeter. (Although maybe Norman Foster's new Hearst Building...)
Also, his Imperial Hotel's famous survival of the great Tokyo earthquake of 1923.
So to get to streamlining: if those GCAs were drawing a parallel to the mechanistic aspects of streamlining / a Miesian interpretation, then the reference to the Chicago School is maybe apt.
The Wright equivalent might be drawing inspiration by watching streamlining in nature: fish or porpoises darting through water, for example. In which case, they owe their debt to Wright, who was maybe
sui generis: perhaps Corbu's ideas on nature chip into him a bit -- but either way, both of them giants who advanced architecture into a sort of formalist-natural stye, giants whose shadow perhaps best looms over the work of A. MacKenzie.
It sounds like, in writing of their desire to break free and develop a style in harmony with the local topography and environment, they might owe a debt to Wright, but I doubt Mies!
PS As far as "American style" or not copying Europe goes, much of the credit for modern design must go to Euros: Gropius, Mies, Le Corbusier, even Saarinen.
Of course, for the Yanks there is mighty Sullivan -- and Wright...
PPS There is a great quote from Robert Venturi I've noodled with posting here to see what everyone thinks of its interpretation and application viz GCA. This seems like as good a place as any: "It is all right to decorate construction but never construct decoration."
Taking a narrow application to the world of bunkering, to me the first part of this beautiful
chiasmus justifies the work of MacKenzie, whose bunkers some on here find too "fluffy," whereas the second part highlights the flaw in the use of bunkers as framing and aiming; e.g., what Fazio sometimes is criticized for doing.
Do you agree? What are wider applications (beyond bunkering) of Venturi's quote?