AST needs an extra instant cast damage spell

[Eloah]

Not a PC thing.
It's all about how the GCD and oGCD work.
When you use instant cast spell, you have to wait until it's ready again (2,5 max and less depending on your Sps/Sks) before using another GCD action. That's the perfect moment to "weave" oGCD, which as it says, have their own Cooldown and can be used in between those small times.

This doesn't answer my, admittedly vague question, so much as reaffirms what you want the skills to do. I guess a better way to phrase it might be why doesn't it feel fluid to you when it does to me and I'm sure other people?