As it's been mentioned, this is after all a Final Fantasy which is typically pretty story driven.

I really hated in FF1 when I had to get the rat tail in order to upgrade my classes cause I had to do a bunch of story up til then.
I really hated in FF3 and FF5 when I had to do the main story to unlock more advanced jobs.
I really hated in FF11 when I had to take one of the 6 starter classes to level 30 before I could unlock any of the advanced jobs. (/sarcasm)

While we're on the FF11 boat, can people stop using that as an example. Yes, you could get jobs and access expansion content without completing the previous expansion. However, you still needed to be level 30 on a base job to get an advanced job, a certain rank in your city to gain access, or a high enough level to clear the fights that locked the content (Promyvions). In FFXI, the simple act of leveling to 30 to accomplish any of these was an order of magnitude more grueling and time consuming than finishing the MSQ in FFXIV.