Interesting. He has admitted that he never liked Phoenix - he found her to be "too powerful" - and was also instrumental in killing her. I will have to hunt for the article - or was it the Chris Claremont documentary? - but I remember reading or hearing Claremont claim that he never wrote the death of the D'bari being caused by Dark Phoenix consuming a sun, i.e., Claremont claims he never wrote for there to be a populated planet located in the star system she was responsible for destroying. He was shocked when he received Byrne's pages depicting the destruction of a populated planet. Furthermore - and this I remember from the Claremont documentary - it was Louise Simonson who wrote the captions for said sequence.
I love Byrne's art, but have been turned off of him by what I've learned over the years.