Uhh what? I've played Dragoon in all of these activities and often.

Ifrit (Hard)
Ifrit (Extreme)
Moogle (Hard)
Garuda (Hard)
Miser's Mistress
Hamlet
Skirmish
Nael van Darnus
Strongholds

Seeing as that is roughly 90% of the games content I think Dragoons are doing just fine. They are on par with Monk and can even do better damage in certain situations (especially considering if the mob doesn't have a weakness to a element Monk doesn't have). The recent revamp of Dragoon make the job viable for almost all content. If your parties/linkshell doesn't use it then it's there fault because I play it all the time, and generally wherever I want with no problem.