The people who ruined Charmed were the people who wrote it. The show was bad from the start, however it was so bad that it was good. None of the characters had depth and the storylines were predictable and everything was nicely tied up in 45 minutes. The show didn't become so bad it was hard to watch until the later years, where it seemed like no one involved gave a ****! While Rose's acting was not as good as Doherty's, Rose did not contribute to the awful writing on this show.

The executive producer was the one who wanted babies, mermaid spin offs, and more make relationships. The WB only renewed season 8 if they added a new witch, Billie, and so you cannot even blame the actress on that one (even though she wasn't fit for this role). I'd say Alyssa and Holly Marie Combs had a slight helping hand as well as once they become executive producers their characters well...Phoebe became a celebrity who was adored by many and...yeah.