Every Franchise That Successfully Passes the Mantle to New Leads Knows This
Franchises have existed since the beginning of Hollywood and filmmaking. Binge-able movie franchises like James Bond, Star Wars, the Marvel Cinematic Universe, you name it, are seemingly here to stay. Seeing as they serve as the bread and butter of Hollywood, studios are looking for ways to keep them going, even as the original actors decide to quit. Studios, for years, have been trying to see if some franchises can move forward without their franchise player.
This change in position works in this hand-off's favor because it doesn't feel like Adonis is Rocky's replacement. Adonis is the main character of this film, so we're attached to him. We spend the first part of the film learning about Adonis, finding out what his wants are, what his troubles are, and what his background is before we are reintroduced to Rocky. Adonis is his own person and not an attempt to copy and paste another Rocky to slot in at the end of the film.
Why Has the Scream Franchise So Successfully Changed Leads Through the Years? Similarly to the Creed/Rocky film, the Scream franchise has been able to consistently change characters and leads. When Ghostface first hit theaters in 1996, Sidney Prescott was the main character and that continued for the following films, but Scream has been able to have a revolving door of characters returning.