Xorn was bad, but that had been ruined long before Bendis ever touched it. I thought Bendis's treatment was a pretty decent attempt to fix that whole mess. I can't see blaming him for any of it - blame Joe Q and Chris Claremont.
Editorial decided that his changes (killing Magneto) were too good for an X-Men story. It was decided to bring Xorn back as an actual person (a story written by Chuck Austen). Claremont brought back Magneto. Both stories were so bad, they made me physically ill.