Owen Eather has appeared to have responded to The Narrow Road as if it was a work of non-fiction. I too have read Russell Braddon's book albeit 40 years ago (non-fiction), my father was evacuated from Singapore and shipwrecked, nearly starving to death, and my godfather was in Changi Jail, so I have some knowledge of that time as well. I have also seen a number of documentaries on the subject over the years. I am not an expert though.
The TV series was adapted from a book of fiction based on some real events and therefore the producers should be allowed some "poetic"license". A documentary which it definitely was not, would have to be realistic and his criticisms might then be justified.
Although not perfect, it was a deeply moving, incredibly sad, and beautifully filmed and acted series.