That's right! In order to even play the new Final Fantasy XIV: Heavensward content or even try out the three new jobs of Dark Knight, Astrologian, and Machinist, you need to play through the entire main storyline from the launch of the game up until the 2.55 patch that was released just last April.
Now here's the catch - the vast majority of that time has been spent slogging through old content from before the Heavensward expansion.