I would think that if they brought back more % based damage that the world would be much more dangerous. Because getting hit for 100 damage when you have 2500 from a boss isn't really harmful, for example. But if the boss hits you for 15% of your health (abilities of course), then it wouldn't matter if you had 250k, it would still be dangerous. I would think something like a 'trap' or 'bounty hunters' would work with this, so there is always the potential of death if you don't pay attention, for all levels. For named quest 'boss' mobs as well.