Zenith skill with Weaken upgrade does not reduce cooldown when using Sunder upgrade.
Sunder is completely bugged. Completely bugged. Sunder bugs:
Frequently, about 40% of the time, while using the 5 set Dauntless Fiath charm set, the afterimages cause Zenith to not cast. Occasionally, the bugged non-cast will do the initial damage.
Zenith + Sunder variant - Sunder does not deal increased damage as the tooltip states. The sunder variant does the basic, non-variant damage.
Zenith + Sunder variant tooltip is bugged. The tooltip’s damage increase goes up by DOUBLE the intended amount when +skills are applied via external methods (items, charms, etc). Instead of going up by 90% per rank, external +skills show up as 180% per rank.
Zenith + Sunder variant - The sunder’s eruption DOES NOT cause extra attacks from echoes.
Zenith + Sunder variant - Zenith’s cooldown does not reduce when killing weakened enemies.
The whole class is bugged. Maybe we have one build. But wtf plays a character for only one build?
I just tested it and killing weakened enemies DOES lower Zenith’s cooldown. I tested with the Sunder upgrade. I suspect the OP made the mistake of trying to have Zenith itself proc weaken, but it only does so on enemies that are not one-hit-killed by it, so you have to weaken the enemies first before you kill them with it.
I suggest using the active of Fanaticism to weaken enemies. Just don’t use the “rite of humility” upgrade (the vulnerable one) because it changes the active to make enemies vulnerable instead of weakened.