Spreading rot gives extra damage if the enemy has been hindered by blight. Aspect of the Spider hinders all enemies in your area of effect. It seems to be that spreading rot bonus damage is applying to all enemies effected by Aspect of the Spider without the need for blight. Moreover, you can still get PoE Trade Currency from us now, and we will offer you PoE guides and tips.
Aspect of the Spider applies Hinder (30% reduced Movement Speed) and Spider's Web (5% increased Damage taken). So the more stacks of Spider's Web on the enemy (default 3) the more damage they take from any source. Could that be the source of extra damage you're looking for instead of Spreading Rot?
I'm pretty sure its the spreading rot from doing a few tests. The damage is way more after adding the jewels. Its not that gamebreaking, but def gives my essence drain build a nice damage boost without having to use blight. Might be OP on other builds tho. Also, you can use PoE buy items, make your Path of Exile life much easier.
Pvp is a really good way to test this kind of stuff out a little more rigorously than out in the field. Take out some of your damage links then try it with and without jewels against someone that can survive a couple ticks of your ED.
Depends on how many more multiplier you have, if you have a shit ton more and not very many increased, the increase would be giving you a huge spike. If you have 50% increased damage and adds 20% increased damage, it's not as a huge spike as if you have 0% increase and add 20% increase damage.