I have a pet theory that states that the decline of the Simpsons tracks with the transformation of Mr Burns from a villain into whatever the fuck they made him into. The big turning point was in Season 10, when he tries to kidnap the Loch Ness monster to make everyone love him. Felt like a different character written by someone who had no understanding of the show whatsoever. Definitely remember it and the Kidney episode as early warning signs, but around 70% of season 10 was pretty good.
Season 11 was just bilge - contains the Spring Break / Kid Rock crime against humanity of an episode. Think that’s the point where I gave up on it. Behind the Laughter would have been a perfect final episode to sign off with, but there was more money to be milked.
If you have 30 minutes then the Super Eyepatch Wolf video on the decline of the Simpsons is pretty excellent: https://www.youtube.com/watch?v=KqFNbCcyFkk&t=18s