In the trailer Mary Anne calls Adonis out on apparently using Apollo as an excuse for fighting Victor... and she might be right. Adonis has never wanted to just live up to Apollo's image; he wanted to surpass it. What better way than taking on and defeating the son of the same fighter that his father not only couldn’t beat, but was killed by?
It's mentioned early on that Viktor fights with "an unorthodox style" in spite of everyone knowing how Ivan fought. In fact, everything about Viktor's style and tactics make sense when you realize how he was trained:
Since the Dragos now live in poverty and don't have access to the facilities and Soviet Super Science that made Ivan nearly superhuman, Viktor has built up more muscle than his father in part because he has to work for a living and can't afford more aerobic activity in his schedule. He's compensated with (even more) raw power for the inevitable lack of endurance he's just not built to have.
Viktor repeatedly uses body strikes to set up his head shots on Donnie, explicitly at his father's instruction. Of course he does! Ivan learned the hard way how punishing repeated body shots are to even the strongest fighters, since Rocky "chopped him down" in their fight. He just took the tactic that worked on himself, and applies it to his son's opponents!
Adding to the above, Ivan learned what it was like to be largely on his own at the end of Rocky IV, and has chosen to ensure that his son never experiences that, as well as supplying enough psychological warfare and game planning that his son can focus on his job and adjust during a fight, instead of sticking with a single strategy as Ivan was forced to against Rocky.
The result? A Lightning Bruiser of a slugger who fights smart, has a strong pre-fight psychology attack run by his father, and who can't be beaten the way his father was, striking at clear objectives designed to hasten the end of a fight... But still susceptible to the classic slugger weakness of endurance issues.
Rocky's fear of Donnie fighting Viktor and his line of "He broke things in me that ain't never been fixed" makes more sense if you (choose to) remember the beginning of Rocky V. Immediately after his fight with Ivan, he's already showing signs of brain trauma, something that's never been seen after any of his fights. Then he discovers his accountant screwed him over and cost him all the money he's earned throughout his career, and cost his family their home. A simple solution would be to have a few fights to win back some of it and keep his wife and son in the home and lifestyle they're accustomed to. However, he can't because the damage from the fight with Ivan forces him to retire and forces his family to return to Paulie's house and from the upper class to the lower class. Fighting Ivan Drago cost him the ability to provide for his family and he doesn't want to see the same thing happen to Donnie.
The Barclays Center in Brooklyn hosting the match between Adonis and Viktor seems a bit odd given that it's hosted few high profile boxing events while nearby Madison Square Garden in Manhattan is a much more prestigious venue with a long history of hosting title boxing fights. However, given that the borough of Brooklyn has both a significant African-American (like Adonis) and Russian/Eastern European immigrant population (like Viktor), it makes sense the promoters would host the event there to draw interest and attendance from those groups.
Rocky’s game plan for retraining Adonis to defeat Viktor in the second fight is risky, but the smartest plan for exploiting Viktor’s weaknesses.
Viktor may be a Slugger-style boxer at heart, but his father’s trained him to fight smart, more similar to a Puncher-Boxer, a notorious hybrid of styles that seeks to control the fight with careful maneuvering and overwhelming power.
Adonis’s regular style, Boxer, is simply going to be overwhelmed because Viktor makes few mistakes, has good defense, and way too much power.
So Rocky has Adonis mix in elements of the Swarmer style of boxing, which is the natural counter to the Boxer part of Viktor’s style... but vulnerable to the power of a Slugger (the Puncher part of the Viktor’s style.)
Rocky and Adonis’s gameplan can’t address Viktor’s full power, but it throws him off his game long enough to make it a war of attrition, where if Donnie can survive the punches that *will* connect, he’ll still be standing long after Viktor’s gameplan has collapsed from exhaustion trying to keep up.
Back in Rocky IV Ivan got the win despite outright killing Apollo even though he blatantly did things like not stopping for the bell and shoving the Ref off when he tried to intervene and he rightly should have been heavily penalized if not outright charged with murder. Here, Viktor hitting Adonis after he was down got him disqualified. The difference? Rocky IV was in the 80s, at the height of the Cold War and punishing a Russian hero for a retired boxers sake could risk political fallback (especially since Apollo heavily antagonized him) if not outright hostility. Creed 2 however is set long after the Cold War is over and Russia had fallen from power (at the time anyway, this was before the Ukraine situation) and the Drago's have fallen from fame and fortune so there would be absolutely no political downside to punishing Viktor hence why he doesn't get the title.
Fridge Horror
After their first match, Viktor left Adonis with broken ribs and a ruptured kidney, peeing blood, in a wheelchair for a couple months, and needing help with many tasks for longer. All things considered, especially seeing what his father did to Rocky, Donnie got off easy. What if he was as brutal, or even more so, than Ivan?
At the end of their rematch, Adonis was all set to actually kill the demoralized and practically defenseless Viktor in the ring. Let that, and all its implications, sink in.
Ivan knew this as well, he was in Adonis' shoes years ago against his father. It's why he threw the towel, he learned from his mistakes.
Rocky's grandson doesn't recognize him when he opens the door for him, showing the extent of their estrangement.
Of course there was no way the screenwriter could have known this, but if Ivan and Viktor were still living in Ukraine by February of 2022, things were not going to be easy for them... (Though since Viktor appears in Creed III, which is set in 2020, hopefully that means at least HE got away.)
