"Did it impact his speeches or prodigious literary output?"
Witten by somebody else and not particularly well delivered

Yet he was awarded the Nobel prize for literature in 1953. I suspect the Nobel Committee know a little more about his standing than an exile that snipes at blighty nearly every opportunity. I am also absolutely certain he was not guilty of plagiarism so wrong again!

It is a matter of public record that .. When demand was high for his newspaper and magazine articles, Churchill employed a ghostwriter.