To answer your question: bosses without a reward chest system got only one loot, so mentioned Zevelon Duskbringer and Dharalion give loot to the person who deals the most damage.
The problem is that since CipSoft introduced Bosstiary into the game, players have been expecting mutual cooperation and assistance. By killing this boss, you have not made it possible for others to get the point in their Bosstiary entry. The solution was to beat the 2/3 HP and let the rest hit with a bomb or a proper carving rod.
There are, unfortunately, cases when the boss has such an amount of HP that the player is faced with the choice: win the loot (with the possibility of getting a rare item) and defeat the boss by one hit, or give it away to the rest of players taking away the opportunity to loot something rare. Choosing the first option you will be insulted and hated, because everyone looks at their own interest and no one will think "ok, you met the boss first, you wanted the loot, your right to kill it", they will only see you as the cause of their "failures". Nevertheless, neither Zevelon Duskbringer nor Dharalion is among such bosses and their amount of HP is calmly enough to get loot and help others.
My suggestion is that if there is a possibility, help your friends or people from your server hunting for bosses to complete the bosstiary, while keeping your sanity though. You are not obliged to make great sacrifices and give loot from every boss in the name of Bosstiary.