This is an observation at max level with stats on par to clear seph ex? Cause otherwise you are comparing apples to oranges cause like any game, you aren't starting the game maxed out, you grow your character to that point.

If SE lowered the GCD that much they would have to lower tp cost of everyone's skills otherwise people in the game would run out of tp witching a minute or less.

A MNK at that GCD reduction would have near instant recovery from GCD at that point...