Nah, it isn't. Rocky's a legitimately great movie. Rocky II is a mostly-boring remake that exists solely to have Rock win at the end. Rocky III essentially gave birth to the '80s movie (for all the good AND bad that entails), while ruining Rocky's character and being more than a little racist about it along the way, Rocky IV is an incomprehensible turd of a film, and Rocky V is even WORSE than that. Balboa is good, but primarily for its dual purpose as a back-to-basics Rocky film and it essentially being therapy for Stallone.
So Coogler being announced to do a continuation of a series that was essentially ended with an old man's well-recieved and admirable public therapy session was seen as "a waste" and "a bad idea."
And then he turned out a movie that stands right next to Rocky, if not slighly surpasses it.