A lot of jobs have off GCD abilities so honestly the combat isn't really slow even with the 2.5 GCD. You are almost always pressing an ability of some sort, be it a buff or a off GCD attack like bloodletter, sidewinder, howling fist, shoulder tackle, blood for blood, inner release, ninjutsu (and this is just some of them)...I mean we have tons of them for multiple jobs even all the card stuff for AST is off GCD.
We also have two jobs with faster GCD (MNK and NIN) for people who really want it even faster. So there really is something for everyone. I also have never heard anyone complain about the current GCD only people who never played the game and the only thing they know is "it is 2.5 GCD" but don't realize the speed really involved for playing a job to high efficiency/skill.