The problem with "Instant OFF GCD" abilities makes combat feel less rewarding.

[VahnValbosce]

It's not... I play warrior and I can use a Non GCD Ability before my Global Cooldown ends.

Example:

Heavy Swing -> GCD -> Foresight -> GCD Ends and I can do Skull Sunder.

You have to time it properly. You get one Non-GCD Ability per global.

This Is STILL Final Fantasy, and still requires thought and strategy, not button mashing.