Given that theme park MMOs are expected to fulfill a wide range of fantasies, it is difficult to argue that *any* features are parasitic as long as they add another facet to the roleplaying/adventuring experience. However, if I *were* to look at parasitic design, I would point toward things like:
* Chocobo Racing. Waste of design space for the sake of three boring courses and unengaging gameplay. (to some extent, also Lord of Verminion, albeit mechanically deeper, is very slow and repetitive)
* The Hunt. I never enjoyed this feature as FF XII's sole extracurricular. But I'm especially perplexed why it exists alongside-yet-separate-from the FATE system (and as currency, separate from GC seals). A lot of bureaucratic red tape inserted for no reason (much like ARR's Relic Weapons).
* Mining/Botany. Weren't fun when they were more complex. Aren't fun now that they are mindlessly simple.
* Multiple crafting classes. Their hotbars all play identically. The quests are functionally identical. They generally share the same gear. I don't know why I need to waste all the time, gil, and weapons slots to do this eight times over. At the very least, Armorer/Blacksmith should have been combined, but I would argue that if the jobs weren't going to be differentiated more they all should have just been a single crafting class.
These things clearly have niche appeal, but I also think they are so thin and/or clunky that they really don't have any reason to exist for their own sake in their present form. I especially think the Gathering/Crafting classes fit the idea of "parasitic" the most since they are so insular in how demanding of your time and resources they are and yet how important they are to the game and community. Even if you yourself don't want the convenience of being able to craft things yourself, the entire game's economy revolves around crafting and gathering.
And again, I have to recognize that my perspective isn't absolute either. To some people, it may be that FF XIV is a game about maintaining a virtual job and playing the local market. Maybe to them it isn't an action RPG but an economic RPG. But that's not how I play it, and at least based off of how the rest of the game is designed I don't see that as being its primary source of fun for players.