Did Lois & Clark begin to decline in quality once Brad Kern became a producer?
Brad Kern became a co-executive producer of Lois & Clark in the later seasons. It was from there, that the show arguably went from being a very clever take on Superman and the Lois Lane/Clark Kent relationship to a goofy, slapsticky show.
Many Charmed fans hate Kern and blame him for that series doing downhill in quality in the post-Shannen Doherty seasons with Rose McGowan. And incidentally, that too was a show with a female creator (Constance M. Burge and Deborah Joy LeVine previously).