I just found this post and have an answer for it…
Actually, I recently noticed something strange with Weaken when I was attacking enemies. And then I did some tests with Weaken and Crit Chance.
First with Crit Chance.
Anything that causes damage has a chance to do Critical Damage, except for Damage from Crushing Blow or Crushing Flames. And this is why Crit Damage is so amazing.
Attack Damage has a chance to do Crit DMG. What is so important about this is that Poison, Fire, and Bleed DoT’s and Arcane Orbit, Fire Immolate, and Poison Toxic are based on your Attack DMG. If your Attack does Crit DMG, Fire, Poison, Bleed, Orbit will be based on the Crit DMG instead of the original attacks damage.
The really amazing thing is that Fire, Poison, Bleed DoT’s and Orbit, Immolate, and Toxic also have a chance to do Crit DMG!
lets look at a Poison attack to show what I mean.
if your attack does 1000 DMG with max Crit DMG…
1000 x 5 = 5000 attack Crit DMG.
Poison does 10% of attack DMG every second for 8 seconds.
1000 x 0.1 = 100 DMG every second for 8 seconds.
5000 x 0.1 = 500 see the difference?
Each DoT has a chance to Crit Hit…
100 x 5 = 500
500 x 5 = 2500 an even bigger difference!
From what I understand, Toxic DMG would be based on Poison DoT DMG before Crit Chance is applied, and it also has a Crit Chance!
100 x 4 x 5 = 2k
500 x 4 x 5 = 10k
Just remember that with +60% Crit Chance, you won’t do a complete chain of Crit DMG with every hit, but it’s a lot of damage when you do. And with Deadly Strike for double Crit DMG, there’s a small chance for a full chain of Deadly Strike Double Critical DMG!
Now for Arcane Orbit, because it works a little differently than the other Elemental Criticals. Orbit can also do Crit DMG, and unlike Fire & Poison DoT, it also can do Bleed Chance (similar to Fire Immolate & Blistering causing Bleed DMG). In this case the Critical Chain with Bleed Chance looks like this.
Arcane attack 1000 DMG
1000 x 5 = 5k Crit DMG
Orbit 1 x 5000 x 5 = 25k Crit DMG
Bleed 1 x 25k x 5 = 125k Crit DMG
Just remember that it’s a +60% chance for the Critical DMG, and the enemy hit by an Orbit would have to both Critical Hit & Bleed Chance from the same hit to get that 125k Crit DMG. And of course, getting a Deadly Strike Chain all the way to Bleed isn’t easy either.
Now for Weaken, which is the main reason I’m writing this.
This is a post on how Weaken works 
What I recently noticed was that Weaken doesn’t just affect your Attack DMG, but also DoT & Orbit DMG! And Weaken can be 100% or higher, which means you can auto chain Weaken DMG from the Attack DMG to the DoT/Orbit DMG!
Now, if you have Weaken with Critical Damage , you can end up doing a lot of chain damage with Fire, Poison, Bleed, and/or Arcane. The down side to all of this is the 2+ spaces needed for Weaken higher than Crystal +90% Weaken.
Although Ignore Resist doesn’t do extra damage, it only takes up 1 space, so you could put other damage multipliers in the spaces saved by not using Weaken 100% or higher.
Blight would increase the damage of Toxic before calculating for Crit DMG.
Blistering calculates Bleed DMG from Immolate DMG before Crit Chance I think, like Toxic from Poison DoT.
Celestial increases the damage of Orbit before calculating for Crit DMG and then Bleed Chance.
Bleed DMG is increased by any Bleed multipliers before calculating for Crit DMG, which is why Bleed DMG can get crazy high numbers with a good Bleed Build.