Joshua would beat him up so badly. Butter bean was a 4 round fighter who fought bums. He’s not in good enough shape to last long against any decent heavyweight.
As a huge "Rocky" fan-& any poster named Carl Weathers will likely back me up on this-I am not disputing your predictions, just your characterization of the first fight in the series. This was not a lucky kd-at most Apollo underestimated his power, but the skill & timing was no fluke. And the way you describe it is opposed to the (un)reality of the story: it was extremely close, both fighters took huge punishment & the announcers said that they looked like they were in a "war" at the start of the 15th round. Which itself was very competitive. If the champion traditionally need to be convincingly beaten, this could have at least been a draw.
Butterbean was a circus act, and never a legitimate contender. His most notable win was against a rusty Peter McNeely, and his only notable non-4-rounder was a unanimous loss against a fossilized Larry Holmes.