> why wouldn’t you also change the damage and other related numbers (such as damage reduction and so on) to percentages as well?
Because a sword might do 5HP of damage, not 10% of anyone's damage (whether they've got 50 or 5000HP). Otherwise, hit points are meaningless: 10 attacks with a 10%-damage weapon kills a lowly serf or a mighty dragon.
And because damage reduction might reduce a fixed amount of damage from an attack. Etc.
Obviously a dragon doesn’t get damaged at all by a puny little sword. You can’t just say that hitting a dragon with a sword a thousand times would kill it, when none of the attacks can get through the dragon’s armored hide. On the other hand, it will die immediately if pierced by an arrow provided that arrow hits the one spot where the hide is missing a scale. The dragon has 100% DR, except in that one spot.
> Obviously a dragon doesn’t get damaged at all by a puny little sword. You can’t just say that hitting a dragon with a sword a thousand times would kill it, when none of the attacks can get through the dragon’s armored hide.
Because a sword might do 5HP of damage, not 10% of anyone's damage (whether they've got 50 or 5000HP). Otherwise, hit points are meaningless: 10 attacks with a 10%-damage weapon kills a lowly serf or a mighty dragon.
And because damage reduction might reduce a fixed amount of damage from an attack. Etc.