
None of the jobs themselves are really "rare" in the current age. The arts themselves may have at one point been lost to the ages, but that isn't really the case anymore. Square made certain to make note of that. Dragoons, for example, aren't really all that rare. It just isn't likely to be easy to rise to the station of Dragoon in Ishgard. Not to mention that when you rise to the rank of Dragoon in Ishgard, you are granted a Gae Bolg by the Holy See. That's basically to be your trusted lance, as it's forged from dragon bone and tempered in dragon blood if I'm not mistaken. Lacking that weapon as a "true dragoon" might have some interesting consequences, and make for interesting background. The only thing that is rare in terms of dragoon lore is the Azure Dragoon, which is just something that you can canonically avoid, since it's a pretty meta-gamey subject to touch on.
Other trades, such as the Monks of the Fists of Rhalgr haven't been lost to the ages. There just isn't as many around as there used to be after the purge in Ala Mhigo. There are plenty of ways for your character to have either met a Monk who escaped, or have been a member of the order who escaped. Hell, you could learn from some one who learned from an actual Monk. That's one easy way to justify so many of a certain job. One person learns from an original source, and they teach two friends, and those two friends teach two friends.
In this age of adventurers, knowledge of the jobs is common place, plain and simple. You can easily justify being any of the jobs. Some might have certain consequences or requirements if you plan on learning from the original source, or being an "original disciple" of the job (like the Dragoon requirements mentioned earlier).
Other trades, such as the Monks of the Fists of Rhalgr haven't been lost to the ages. There just isn't as many around as there used to be after the purge in Ala Mhigo. There are plenty of ways for your character to have either met a Monk who escaped, or have been a member of the order who escaped. Hell, you could learn from some one who learned from an actual Monk. That's one easy way to justify so many of a certain job. One person learns from an original source, and they teach two friends, and those two friends teach two friends.
In this age of adventurers, knowledge of the jobs is common place, plain and simple. You can easily justify being any of the jobs. Some might have certain consequences or requirements if you plan on learning from the original source, or being an "original disciple" of the job (like the Dragoon requirements mentioned earlier).