I think you would also find that many other scholars have made the connection. I have not done the research independently, but many writers at the time also, including--for example--Robert Graves--made the connection, and it is the case that seances were held to speak to the War dead. That it was not new because of the War does not mean the War did not make it a powerful cultural activity. Yeats and many others were into it before the War, but those who sought solace from death found that it seemed a last hope.
“The Birth of Modernism: Ezra Pound, T.S. Eliot, W. B. Yeats and the Occult” by Leon Surrette.
This is an excellent book which, if read, would lend some rigorous authority to the speculation of this list. I think for one thing that readers would find that the occult fascination of the modernist predates and is little related to world war I and its horrors.