I would say it is number of episodes more than just years, as a show with 20+ episodes per year will run out of the same number of ideas twice as fast as 10 per year, and the latter has more time available to think up and refine ideas.
I would say long running shows should be the exception to the rule, and all those shows that drug themselves out for whatever the syndication minimum was are the best examples moat things having a limited lifespan. Plus the number of years tends to lead to staff turnover and the people writing season 7 are most likely not the same as the ones who made the show successful in the first place.
I would say it is number of episodes more than just years, as a show with 20+ episodes per year will run out of the same number of ideas twice as fast as 10 per year, and the latter has more time available to think up and refine ideas.
I would say long running shows should be the exception to the rule, and all those shows that drug themselves out for whatever the syndication minimum was are the best examples moat things having a limited lifespan. Plus the number of years tends to lead to staff turnover and the people writing season 7 are most likely not the same as the ones who made the show successful in the first place.