Nadir Mode prevents the skill from getting Intensity

I use Hexblast of Havoc with cast speed 0.25sec, without Nadir Mode I can stack Intensity without any problems, it reaches 4 stacks in 1 second. With jewel, my stacks are fighting between 0 and 1, which does not have sense with my current cast speed.

With a 0.25 second cast time, and Spell Echo Support, it should be taking 2 seconds to reach 4 Intensify stacks.

Wiki sources:
Intensify: "Repeated casts do not contribute additional intensity."
Spell Echo: "A repeat is part of the original cast. It ... does not cause when you cast effects to occur a second time."

It takes 0.25s to complete the first cast, 0.25s to complete the repeat, and then you can start a new cast--but Nadir Mode makes you lose 1 stack per 0.50s, so you have little to no net gain.

Oh thank you, this makes sense.