Why not borrow the good parts from FFXI?

[Alash]

Because the game design does not allow for it.

-Massive city battles with invading forces.

Would result in, and I quote yourself, "100s of people running from nm to nm killing things near instantly, and lagging people out."

-Ferry/Raft rides with random events

In XIV would turn into "An instanced 'dungeon' where sometimes a giant crab spawns, and sometimes it doesn't. And the giant crab drops lv.1 glamor gear."

-Meaningful exploration with difficult mobs, mazes, unique pathways, and things to discover

I doubt this game can actually do this. You have to remember that part of the reason XI felt like this is that
A) You sucked at it. You were a ween who'd hardly played an MMO let alone an online game and didn't fully understand the constrictions the medium possesses, and...
B) You were probably still on dial-up or really crappy ADSL and so you weren't inclined to seek online sources of information out, or maybe didn't know of their existence. Not to mention today's datamining culture literally everything in the "maze" would be discovered before the servers even come up.

-Skill-based battles rather than combo-spam

Would require an entire rework of the game systems, something I doubt they are inclined to pursue.

"I don't understand why devs keep implementing the same 100+ person spam hunt/nm/fate mechanics"

Because their subscriber numbers stay afloat, so why bother improving? The game has remained exactly the same since 2.X, and it isn't going to change.