Dungeons are becoming style over substance.

[Packetdancer]

Same goes for FF14. I've done every dungeon in the game scaled down throughout playing and I can safely say I see nothing in the older dungeon design that would've ever made them complex.

Allow me to introduce you to the Nanawa Mines:



Or the Mun-Tuy Cellars:



The original Aurum Vale and Dzemael Darkhold weren't nearly so complicated as those two, but the 1.x versions were certainly worlds more complicated (and larger) than their current incarnations.

Now, I'm not saying that these were good dungeon designs -- witness my own posts in this thread from a few months back about the flaws in 1.x dungeon design -- but I definitely think they count as complex.

HOWEVER, as noted, people generally didn't go through the entirety of those dungeons, at least in my experience. They tended to figure out what the optimal path was and then take that path, consistently, avoiding all the side passages and optional stuff.

The original Aurum Vale had three potential diremite bosses to fight -- three variations on the boss currently there. And if you were good, you could get every photocell and open every pathway and fight all three diremites and get loot from each! But basically everyone I know ended up taking one specific route -- the shortest one -- to get from the entrance to a specific diremite as quickly as possible, get the loot from that, and leaving.

Yeah, single hallways are more accessible. But we've also demonstrated that, as a playerbase, if the devs give us a complicated dungeon we'll figure out a way to turn it into a single hallway full of enemies leading to a boss fight anyway. Because that's the fastest way to get the shiny prize at the end, and we as a playerbase seem kind of fixated on optimizing our instanced duties.

Whilst I don't necessarily disagree with the idea of this. I just have concerns about practicality. The inevitable result is that people will always go for the most efficient route of completing a dungeon. If people don't need the explore something, then they will rarely bother to do such. I can pretty much use Haukke Manor as a feeble example of this.

See above.