Disclaimer : I'll admit that I loved FFXI, more than any other MMORPG. But I don't think my opinion is biased in this.
The problem is not FFXI inspired content, the problem is the execution of it.
First they release Palace of The Dead, largely inspired by something called Nyzul Isle Investigation.
Nyzul Isle was a challenging content for a single party. And it could indeed be very challenging, due to it's random nature. But it also gave great reward and was a necessary part to get Mythic Weapon Skills (powerful new abilities) and Mythic Weapons (FFXIV relic x100).
It was limited (one entrance tag a day). And, most importantly, the requierements to get to the next floor were much more prominent. (Kill a boss, a specific monster, a monster family, activate lamps in different ways etc.)
So they turn a HL content that was difficult, rewarding and much more diversified, to a mindless bash of random ennemies with no subtleties at all and overall poor rewards.
And then Eureka. Eureka is nothing like any content in FFXI I know.
I honestly don't know what they were trying to emulate with this one...NM/HNM camping ? I'm pretty sure no one here was asking them to take that from FFXI. While it has it's pros, it was certainly one of the most daunting side of FFXI. And even so the incent for camping an NM for hours, even days, was incredibly superior to what we get in those fate. Thanks to the horizontal progression system, you could be getting an item that would last you forever, sometimes on multiple jobs. So while the experience was far from fun the reward was, for some people, well worth the grind.
So here again, the problem is not FFXI, but the way the handle things here, in FFXIV.
And let me tell you, FFXI had a lot of great features that could be transposed very nicely here. But they had to do it right, not just copy paste the concept without all it's flavor.
The best features that, I think, could do great in FFXIV if done right, are ZNM for open world content, and Sea/Sky for Eureka-like instanced content.
Both are challenging group/alliance content that are, in my opinion, far more interesting and rewarding (gameplay wise) than this FATE train crap.
But for this, and any other content, to work, they have to really think about what made those content fun and interesting.