Not so. The influences of Koestler upon Orwell are obvious if you keep the relative publication dates in mind - 1940 for Darkness at Noon (with author's notes dating to 1938); 1949 for Nineteen Eighty-Four. In his essay, Orwell makes them more plain. Orwell's book reviewing style proves more than anything else that he is a man born to write. He gracefully reveals his own philosophy in every paragraph in a manner which never detracts from the topic at hand. And of course he is the master of the British-style understatement:
We forget these things now, but a quarter of a century ago it was confidently expected that the Russian Revolution would lead to Utopia. Obviously this has not happened.
The most important part of the essay is the passage near the end starting with "To take a rational political decision one must have a picture of the future...." These three paragraphs lay bare the central problem of 20th Century politics. It is breathtaking that so much could be said in so few words.
I recommend the essay to everyone interested in either writer (and I recommend that everyone become interested in both writers).