That's because the weapons of others are either dependant on max HP or max MP e.g. The closer it is to Tidus's max HP, the higher the damage output when wielding the Caladbolg. It kind of follows the same tradition to other old FF games, whereby the strength of the weapon is governed by certain variable factors such as what has been stated above. In the case of Auron, his Masamune is similar to the way Locke's Valiant Knife in VI operated.ohhh i didnt know that ow come all of the other wepons dont do that ??? wait he can sometimes do 99999 with full hp without it being a critical hp
As for what happened in your situation, my guess is that you may have landed critical hits on the opponent concerned or that you came up against an enemy with little or no inherent armour protection. Critical hits is correlated to your Luck stat, the higher it is, the greater frequency of critical hits you’ll stack up in battles. For the most part, you can tell when a critical hit has been executed as the sound effects are different to that of a normal hit.