Just to be precise: Fire and Poison are similar even in output damage. They are both damage over time, but in different ways. Fire is much more faster but ends before than Poison. In 1 second, Fire deals 3 waves of damage. So for each second it lasts, Fire inflicts 3 times the same flat damage. For instance: assuming you'll inflict the Scorched status effect on a enemy and supposing Scorched status lasts 6 seconds, each second you deal (example) 3x100 of Fire damage (first wave 100 dmg, second 100 dmg and third 100 dmg). Totally, you'll inflict 1800 fire damage over time (divided into 18 waves). Poison instead deals 1 wave of damage in 3 seconds (just one). The flat damage of the unique wave is superior than the fire one (but of course fire is 3 waves per second).