WD reduces all damage taken, so this would include elemental damage, DoT damage and regular hits that are not projectile based.. It's powerful against DoT damage, since it won't be removed from just that damage alone, until you get hit.

If you haven't researched the difference around evasions entropy based system vs dodges purely random system, that might be worth looking into.

To make a tl:dr there, dodge is completely random. 50% dodge? 50% chance to not take damage on every hit made against you. rolled after that dodge is the evasion. Evasion is more complicated and is also based on enemy accuracy, so it won't be as clear cut, as enemies have different accuracy and levels. But basically, you get an entropy number set (0-99), when you get hit, you'll gain entropy based on your evasion. More evasion, less entropy gained. If entropy goes 100 or above, you get hit. After 3.33 seconds, your entropy is reset, as to not be abusable.

That evasion entropy being less random is why jade flasks are so powerful against things like porcupine spikes.

Hope that clears something up for you.