You're showing a severe lack of critical thinking here. Everyone knows that different people find fun in different ways. No one will argue otherwise.
That however does not remove the concept of fun as an important and viable metric in content design no matter how much you wish it so.
For instance you probably found Eureka fun, and I found it to be one of the worst developed pieces of content I've ever seen across a decade of MMO gaming.
But here's the thing. It didn't have to be that way. I could have had fun too, if they actually designed something in the zone for a player like me to do, but they didn't...
FF14's needs to stop designing content for specific skill levels in an isolated fashion. It's an incredibly inefficient process and equally as juvenile. Grinds only artificially boost a given content's lifespan. When designing content they should be aiming to make each endeavor as robust as possible to offer multiple viable avenues of play.
If Chocobo Racing was Mario Kart/Crash Team Racing on Chocobos with summons and magic, it'd be really solid; fun for a lot of people. If it came with PVP and PVE matchmaking and a time attack mode even more would like it. If it had a level editor and shareable designs, you'd find even more people like it. THEN you throw in some cool rewards (speaking personally if I was the dev in charge, I would have put the entire chocobo coloring scheme and a ton of bardings behind this system, but alas they decided menu content was a better idea).
In the first sentence you get some people who like it. Adding matchmaking gets even more (without affecting the others), then you add a time attack mode to grab people who want to just race themselves, and then you add a level editor for people with a lot of free time and creativity, then you put some decent rewards in there to get the rest.
Do you get my point yet? You can design content for the bare minimum common denominator or you can design robust content.