First of all, I apologize in advance, as this question has probably been asked before...

Is it viable to level your primary class doing mostly your main quest line, and FATEs?

I admittedly have little understanding at this point on how the job systems work, but if I do need to "grind out" multiple classes, I'd like to leave as many side quests behind as possible to make that quicker. So far, because of the population density in the low level zones, I've been doing a lot of mob grinding for exp to make up levels, since I can't get to FATEs before they're completed most of the time.

Thanks in advance for any input on this