I'm not so sure it's all about job design. Encounter design plays a significant part in the feeling of flatness, too.
Some of each job's uniqueness gets watered down by encounters not really requiring anything in particular. Back when HM Ifrit wasn't laughably overgeared (and Eruptions hit harder), you could work out a stun rotation if you didn't have a PLD to stunbot. In T1, you got to play around with BRDs & PLDs & MNKs for silencing, depending on what you had.
I'm sure there's some of this going on in Coil 2 now (SMNs kiting? Or something?), but outside of that, almost every encounter is the same. Your role in the fight is encompassed almost entirely by your role in the party list: tanks tank, DPS DPS, healers heal. Everybody dodges. It's sort of a Catch 22 between a lack of unique utility skills and a lack of need for unique utility skills.