There's no difference. They're both silky smooth (if you consider a longer GCD not smooth, then you're not using the right words) and both combat systems work flawlessly. Your combat times are based AROUND your GCD, so it's not a hindrance when it's designed that way. Even leveling in the new expansion for FFXIV, depending on your class & I was playing the new Samurai which was considered OP at the time, it was still hard to do 1 mob, taking on two mobs that are intended to taken on 1 on 1 is very difficult. There are mobs, usually in quest lines, that spawn a bunch of enemies but their health is made lower to make up for it otherwise some fights would be straight impossible