Honestly would it be such a bad thing if the show only went for two or three seasons?
A show overstaying it's welcome is far worse than a show quitting when it's ahead
5 seasons is pretty much the ideal length as long as the people in charge have an idea of what they are doing
Obviously sitcoms don't have to worry about that but I still say the Simpsons should just end
Depends. Most shows overstay their welcome becuse of bad writing, which is a very common thing on TV. A tv show becomes popular becuse they are doing a good thing, and then they play on those cards for too long without changing.
Buffy the Vampire Slayer has seven seasons, but it is not one episode too long. In fact, the show could have used more episodes. After the third season, they changed everything in that show. To the point where it felt like a completly new show. In season 5 and onwards the show changed again, and was nothing like it old self. Yet, Buffy had never been so good, and Buffy was a 10/10 show in season 2 and 3. Superb and masterful writing.
Then you have shows like HIMYM etc who plays on the same cards for way too long, and in the end it just feels like the same thing but it is not as funny anymore. Very common for "crime of the week" shows like CSI etc. Even Supernatural has fallen into this trap.
Clark Gregg described the setup in the post-Avengers world, where ordinary people have suddenly become aware of all the extraordinary beings around them. What Joss Whedon said at the end was very encouraging to those of us who want connections to the films: "The series takes place now. The series takes place where we are in the Marvel Universe. And hopefully there'll be some -- a little weaving in and around the movies that are coming up."