I think a lot of people don't give this show credit for recovering from the Dayman popularity boom/bust. The show seemingly peaked with the Dayman season, and they did the whole tour of theaters with Dayman stuff and all of a sudden the show had sponsors like Coor's and everything felt contrived and awful in the proceeding seasons. They lost their way and it seemed like it was going to be a classic jump the shark moment and they would be done. They took time, re grouped and did a great job of bringing the show back to what made it great while also opening up to much more risky and "out there" episode story lines that didn't make the mistake of just being a silly premise, but were driven by the core character personalities they developed through the years.
I agree that it feels like Sunny, had a phase where it was only getting worse, but the fact that they recovered, something that almost never happens with comedy shows was wildly impressive. They could have gone the Chapelle Show route where the popularity and hype suffocated it and just quit before it got even worse, but they managed to put out some of their all time best work post Dayman popularity peak. In addition to the this wonderful finale, the Charliework episode from a season or two previous, was probably one of the most expertly written, directed, and acted episode of a comedy show ever.