I like your analysis, however it's flawed. Drago took Rocky's best punches and they barely phased him at all. Rocky was notorious for having the best 2nd winds (and 3rd, 4th, 5th) and found lots of power in the final round that sent Drago to the canvas. If that didn't happen, Drago wins by UD. Drago had a great chin and fantastic stamina.
Now, I will admit Clubber is stronger than Rocky, but not by much. Clubber's main problem is lack of stamina. His fights rarely went past round 5 and you could see his last fight with Rocky he was out of gas by round 3 or 4. Drago could take Clubbers punishment early in the fight, but Clubber would punch himself out and that is when he is most vulnerable. Drago would still have plenty of energy to throw those monster 1700 psi punches and would knock the gold out of Clubbers teeth. He would die in the ring.
Drago, KO round 5
Clubber is a gangster though:
Little is known about Clubber Lang. Before Rocky's fight against him, he is introduced as being from Chicago, (his nickname is "The Southside Slugger"). According to his bio in Rocky: The Ultimate Guide, James Lang was orphaned at an early age, and spent most of his childhood in the streets of Chicago, orphanages and juvenile facilities. Later as an adult, Clubber was sent to prison for five years, for one possible count of a felony and/or assault charge. But during his time being served he discovered boxing as a way to let out his frustrations and talent, which leads to the events of Rocky III. This is also evident in the game, Rocky Legends, to where if you select Clubber's path, he starts out fighting in the Chicago State Penintetiary, in a ring actually inside the prison itself. The Internet Movie Database does not provide a name for his manager, though one novelization of the film called him "Donut."