Definition of 'Showrunner'
the person who has overall creative authority and management responsibility for a television program.

Mike Scully on The Simpsons. The show lost its wit and satire, and turned bizarre and nonsensical. The humor became a lot more sophomoric and absurd, and characters like Homer became childish and snarky.

It's gotten better over the years, but it still doesn't match the same charm from the first five or six seasons.

Yeah, I hated the Scully era of The Simpsons. Although I think it’s worse now - Al Jean has been there far too long.

I remember Patricia Green taking over “L.A Law” from David E. Kelley, and the quality (and ratings) of that show just plunging. She was fired mid-season during her only season in the job.

I thought “Cheers” became much less consistent when Cheri and Bill Steinkellner took over from David Angel/Peter Casey/David Lee (who left to do “Wings” and went on to run “Frasier”). But I wouldn’t call them the worst. Just disappointing.

Jeff Frielich, the producer of “Falcon Crest” for seasons 6 and 7 is my nominee for the worst. He bragged about never watching any of the previous episodes, brought on terrible new characters, repainted the main set, and replaced the orchestral score with synthesized music. Overnight, he turned a restrained gothic serial into an over-the-top, cheesy, campy mess.

Mike Scully on The Simpsons. The show lost its wit and satire, and turned bizarre and nonsensical. The humor became a lot more sophomoric and absurd, and characters like Homer became childish and snarky.

It's gotten better over the years, but it still doesn't match the same charm from the first five or six seasons.
Mike Scully, in my opinion, has a very weird track record. If I remember right, he was the showrunner for ABC's Complete Savages and that show was pretty mild and down to earth compared to his previous show, The Pitts.