FFXI Content lasted so Long because you had to do it in Phases.

Sky - You had to kill each Boss Once Then you got to fight the super Boss

Dynamis - You had to Beat Each one to move to the next level

Sea - You Had to Beat Each one to Unlock the Next Tier

Nyzul - You had to Beat Each Floor to Move to the next floor

On top of having these built in tiers, each event also had a strategic cool down. Dyn was once a weak. Sky had Pop timers. Nyzul you had to wait for Tags.

People call these times sinks, but what they really did was Push players to work on all of the content simultaneously. You couldn't just throw yourself at the same thing until you figured it out or got lucky.

FFXIV has nothing to advance in. It is all one shot content.