You would need to remake entire netcode on the SE servers if you want to implement faster cooldowns.
You need also to consider the 0.5 global cooldown on all abilities, there is a time gap between you could press buttons for the reason of the SE server managing and even struggling to keep up with 500 ms latency between players and servers.

With the current ogcd and gcd between them you have a chance to active cooldown ability, with 1.5 sec between the ogcd - skills speed, it will be problematic from the technical point of view to let players use a GCD > OGCD > GCD

And yes i believe we need much more CC in this game, especially the AOE CC on tanks that would help them managing the pulls.