uhmm do you already find the answer to your questions? 'coz if not i will answer them. i think you need to search on google mma weight class to understand the distribution. also, weight classes are used in sports to make sure the competition is fair and safe. they help athletes compete against others who are about the same size, so no one has an unfair advantage because of being much bigger or stronger. imagine you being a 40kg fighting against a 90kg, the advantage it brings to your opponent.
I like that Mingwa is keeping it accurate to real MMA weight classes. The MMA has 14 weight classes, with light heavyweight being classed as over 195 to 205 pounds. Jaekyung is 198 lbs, and after he lost weight he was 184 lbs. So, he lost 14 pounds by the fast weight loss before the match (aka "weight cutting"). Weight cutting is fairly common in combat sports and can be dangerous. I read that deaths have resulted from it, which is why some places ban it.
That may be the average weight, but there's still lighter and heavier men than the average who participate in this sport. The MMA's 14 weight classes covers everyone. Potato, for example, is only 130 pounds and he's classified as Bantam weight (over 125 to 135 lbs). Jaekyung's lowest weight was 184 lbs, so he never got down to 80 kg (176 lbs).
There's one thing I didn't understand. In character profile Joo Jaekyung was 90 kilos and light heavyweight (how is that heavyweight? Even if light...) but after loosing weight for match he's 80 kilos (how's that middleweight?), the point is... WTF are these classes? And wtf with that weight loss?