I would venture to say that as the minhag started it was keneged halacha
You are being ????? ??”? ?? ????????, and at the same time arguing on all of those you mentioned above who do justify it.
The reason the Gr”a tried to reinstitute it was because he disagreed with the reasons mentioned (or held the reason no longer applies), and since minhag does not trump halachah, held we should duchan.