Basically you're suggesting a hybrid between Musketeer and Marauder.

The main problem with this is that a class is a specialization in one weapon type. Example: Marauders are axes, they could potentially get one handed axes for a 2nd job. Musketeer will likely specialize in pistols but they could make it specialize in guns in general allowing a 2nd job off of the class to use rifles.

The other problem is this game uses "pirate" in a different way. Marauders are pirates and likely Musketeers will be too. It'd be kind of odd to have a class called Pirate that is also a pirate alongside MRD and MSK. And then you also run into the issue if they give Corsair as a job to Musketeers.