I would dispute the claim that Usyk’s punches were doing nothing. You can ask any one of his previous opponents and they’ll tell you that those punches are both relentless and exhausting to deal with.
When I say "nothing", I don't literally mean "nothing", he's a heavyweight boxer. I mean relative compared to what Fury was hitting with, and also relative to what Fury can take, being the size and mass he has etc. He can take a hit better than most it seems.
100% agree with it all adding up though, it can't not do that, it's not possible otherwise. It's a combination of the accumulation generally, same as anything in life. But also any one large event at one instance can also outweigh the typical single instance if it breaks the single tipping point, i.e one knockout punch is going to probably be worse than 5 punches which may otherwise cumulatively be a lot more.
As for his other opponents, he's only fought 4 heavyweights before Fury, and 5 fights, and he got his belts fighting Chisora and Joshua. Neither of those are not exactly well known for being able to take a hit, and the three fights with them all went 12 rounds, just like the Fury fight did. It's not like he's fought any heavyweight at their peak either.
Not at all saying he's not a great fighter, nothing like that, but I don't think he's a heavy hitter, seems more of a points merchant (which is to be expected coming from cruiserweight), who's timed his accession extremely well.