Some jobs have a longer cooldown. Our stun is on GCD so we can use it ever 2.5 seconds.
Also with DPS I would rather have them focus on killing Ifrit, avoid using their stuns and make sure the nails are down.
Once you know the timing and patterns of Ifrit you can actually use your skills, and once you're good enough you can solo tank and stun Ifrit.
I haven't solo'd tank him from the beginning yet, but I've picked up Ifrit after the War/Pld tank died and tank over half the fight while stunning.

I know it's a boring ass job, but I would rather have one person (who doesn't do much dps) focus on getting every stun then taking the chance of a dps doing it and not having their stun available because they just used a skill.