Jumped the shark?

I thought the first 4 seasons of Mr. D were awesome (awesome, awesome), but the show is going downhill fast. After Principal Callaghan retired, the show lost the dynamic of "Cool principal/uptight vice principal," and I don't really like Lisa as the principal. Also I think Frank and Nisha are bland characters that don't add much to the show, but I do think Emma is a vast improvement over Mr. Leung. Plus, I realize that kids get older and graduate, but I miss Maya and Jimmy.

But mostly, the show has gotten too unrealistic to be believable anymore. Gerry has become "Flanderized" from being incompetent and insensitive but with some loveable redeemable qualities to him, to mean-spirited douche who should have been fired if not arrested long ago. And there have been a few really strange scenarios recently:

-Lisa and Gerry getting married (and staying married)
-Amanda-Susan getting struck by lightning
-Simon's mother dating a guy who looks exactly like Simon

I still like the show and will continue to watch it until the bitter end, but it's not the gold it used to be.