The guy has more than just the advantages of weight and power. He's chemically enhanced with the right amount of alcohol (lower inhibitions, relaxed muscles and positive adrenal dump). He's also trying to really do damage when he strikes. The willingness to do more damage than your opponent is a real advantage. Doormen don't train to fight, or even train in self-defense. Their hands are tied by the law - they're just regular citizens and they can be arrested and charged with assault, as they often are. They are trained to talk down a situation and de-escalate it though. In this situation, the heavy guy is outdoors and off the premises. 99% of doormen would consider the job done at this point, and wouldn't be looking for a fight. Also, from the video, it seems the heavy guy just has one technique - a wide haymaker - and I wouldn't be so sure he's a boxer.
That said, the main point of the OP stands in my opinion.
That said, the main point of the OP stands in my opinion.