Maybe you should read the EW article just a few posts ago in which she explains the timeline for the work on The Vision instead of calling people unprofessional and incompetent without knowing the details. The official work on the book began late last year, and they had been working non-stop ever since. It was a 6-issue mini and they had most of it done already, two months before the first issue was even out, which suggests that deadline was not going to be a problem.
Retconned into a cheater, yes. Into a murderer, no. The scene in which Phantom Rider died was never retconned. Everything that happened there is still canon. Why is it so hard for people to understand that? The guy was trying to kill her and she didn't help him up when he was falling down. If you consider that murder, then she was always a murderer. The retcon didn't change that.