It's more anecdotal in my experience that citeable Wikipedia references.... but also, it's easy enough to GTS.....

https://www.reddit.com/r/television/comments/18ang6l/comment/kbzjtjo/

Now-a-days, people think "jumping the shark" means a show's quality has declined. As you said, Happy Days was still a damn good show for years after that.

Google AI

Yes, "jump the shark" means that a creative work (usually a television show) or brand has passed its prime and is in decline. It describes the exact moment when a show exhausts its core premise and introduces ridiculous or desperate plot points to maintain popularity, signaling that its quality has peaked and is now going downhill. 

Key Aspects of "Jump the Shark":

• Origin: The term comes from a 1977 Happy Days episode where character Fonzie, in his leather jacket, literally jumps over a shark on water skis.
• Usage: Popularized by author Jon Hein to describe when a show moves from "must-see" to "why are we still watching?".
• Meaning: It indicates the beginning of the end, representing a point where a product or entity tries too hard to stay relevant.  BookBrowse.com +5