I don't see this movie as a fail. We got three strong female characters, counting with the other huntress, the blond one (*without a name*). And from the beginning I was not against Etain. The Romans were cruel, the movie shows it all the time.She has all the motives to hate the Romans and I'm quite sure that part of the audience was dubious in supporting the "hero".
I liked the movie. It did not score all the Bedchel Rule, but was fair with the women in it.
'Centurion' = epic Bechdel fail, which is a shame considering the film is by Neil Marshall, who directed 'The Descent' - perhaps the only female-centric (and actually really good) horror film I've ever seen.