As an RPer with many characters I know the dilemma. Most RPers don't like Mary Sues that will just say they can do anything just because the game lets you, but if you do have exceptional abilities, having character flaws to mitigate them help balance that. Fernehalwes also said that even though there is extreme rarity of some jobs by the Storyline Quests, that isn't the ONLY way you can obtain those jobs, so a lot of RPers spin stories like if the Main White Mage they're actually just Conjurers, or they learned the magic another way (For myself, Terrini learned White magic through Echoes of the past.) or some people say they learned a similar art from Doma/Othard or some other far away place.

There are also RPers that RP unique mixes of character skills of their own creation, like I know someone that role plays a magic machinist with magic bullets and a slightly different take of the machinist aesthetic.

I also have another character that is a Paladin, but thematically, Dark Knight seems to suit her better, but the sword and board aesthetic works best for her style. She's not to Ishgard yet though so she can't even get Dark Knight but I'd like to bring that into things. The main thing is in RP you can do anything your imagination lets you, but since it's a community thing you shouldn't go overboard or people will be annoyed with you for it. Just work in moderation and discuss with the group you play with. ^_^