As expected of an S class Inheritance skill. As the level grows higher, the stronger the skills will be. Luckily that skill effect had taken percentage into account, or else the skill could be extremely useless against highly-leveled bosses with more than millions of HP! Zhang Yang would have to grind his way slowly and only use the skill when the boss drops below his own HP! By then, the boss would already be dead.
As a tank, especially during a boss fight, Zhang Yang’s HP will fluctuate up and down between 50% to 80% depending on the healer present. It will be a rare case where he would be at full health. As such, the skill {God of War Heavy Axe} would need to be timed precisely in order to deliver 300% damage. A careless miss and he would be dealing normal damage to the boss.