Are you using Rocky II as an example of a superior sequel, or Star Trek II as an example of an inferior sequel? Because, either way, I have to disagree on at least one count. Not that the law of diminishing returns is usually wrong. Most sequels are less than the films that came before.
I call bullshit. There was no "Rocky II" there was only the original and then the "Rocky Balboa" follow-up that came out a couple years ago. There was no other movies in Rocky franchise.
No.
None.