Usyk makes up for his slight lack of power with his outstanding technique, speed and defense. With my compatriot Hrgovic, the problem was a lack of punch power and imperfect technique, his punches can be precise, but he did not have the power to knock out Dubois, which Dubois used and stopped him...
Hrgovic also has issues with stamina... He's a cast iron chinned points fighter with a 6-7 round gas tank and only mediocre power - that works up to a point, but if the opponent doesn't also have a crap tank (see Zhang) then the path to wins gets difficult very quickly. Fury and Parker never had mega power either, but both have been able to get pretty near the top just by being durable, strong points scorers and having decent gas tanks by the standards of the division.
Just recently, the Wardley vs Huni fight would have had a much different outcome if Huni had an ounce of power. Like you said he had to be impeccable to win without it..
The most important thing for HWs with no power is a steel chin. Otherwise you win the rounds if you win the rounds. I do not think people looking at Dubois v Hrgovic and coming away thinking Hrgovic is Justis Huni is fair. He had success against possibly the best HW who was not expected to be that good at the time. Calling Hrgovic a "point fighter" is also probably unfair. Hrgovic isn't one of the most powerful guys in the division but he hits harder than 3 of the 5 current HW champions. The exceptions are Dubois who has the 2nd highest KO rate of any HW champion ever. Wardley who should not have gotten a belt for beating Huni and who is way more limited than Hrgovic. Hrgovic is also taller than Kabayel, Usyk and Parker.
Yeah, if you don't have big power in your division you have to be an endurance athlete and be tough. And if you have low power for the division you better be unbelievably fit and tough. If Usyk had a bad engine, Fury would have ground him down, maybe AJ would have stopped him too when he slowed down too much. If Usyk had a bad chin, Fury would have KO'd him the first fight. Also if Fury had a bad chin and engine Wlad would have won. Wlad was in fact counting on him slowing down so he could KO him (also thinking he couldn't take a punch). Usyk and Fury are very similar really. Dubious has power but he has engine and chin problems so that's why it should be funny when more fighters take him to 'deep waters'.