Aside from his rumored influence on the decision to get rid of Julie McCullough and the making of Chelsea Noble as his permanent love interest. They also supposedly lost three showrunners and a director over clashes with Kirk. By Season 5 (when Julie was fired) the show's ratings (https://en.wikipedia.org/wiki/Growing_Pains#Episodes) was already in decline and was no longer a top 10 show. And while Kirk Cameron may have been popular among teen audiences, he hadn't really proved himself to be a star beyond the role of Mike Seaver.

He got way too preachy and pushy with his religious beliefs.