I think when people say they want content XI style they mean structured stuff not an exp party.
For example Sky, Sea and Dynamis Were all massive grindfests but the key point is they had structure. Something that's missing from all of XIVs endgame. XIV is pretty much enter an instance arena kill a boss and done or go back and enter again if you didn't get a drop... no structure to any of it as it's all pretty much just single instances.
Compare to Sky for example in XI. Your group would go up there and begin by grinding the hell out of robots sometimes for an hour or 2 to try and make an nm pop (Despot) then you'd go and grind Golems for maybe another hour or so to make another nm pop. Or weapons for another one. Each of these grinds had an objective and a purpose. And it was all structured. All of those nm dropped keys.
If you got 2 keys (I'll use keys for simplicity) you could then unlock and fight one of the bosses which then gave you a seal if you beat them. And once you farmed all the keys and defeated all the 4 bosses you were then able to use those 4 seals to spawn the god boss Kirin and fight him.
Dynamis was also a mega grind but once again structured. Work your way through a dreamworld Bastok or Windhurst etc. slowly clearing the zone defeating bosses for things like time extensions and currency along the way. It was a grind but not brainless there was a strategy involved if you didnt want to get your entire group wiped by pulling the wrong thing at the wrong time and thus blocking your path. in dynamis a wipe often ended the run for the whole day as you couldn't reset or recover.
Sea was kinda like Sky with its jailers. But there was also Limbus and Einherjar again structured endgame. Einherjar you had to clear 3 wings before you could advance to the next 3 and those before the final 3 and only when you had the feathers from all 9 could you go and do battle with Odin..
Limbus was the same had to clear sections of Temenos or Appolyon depending on whether you were after Ultima or Omega. And collect the keys from all the sections in order to unlock the bosses....
Virtually all of FFXI endgame was a grind but it had structure, objectives and progression. And I think that's what people want when they want XI style content. Not diadem 3.0 merit party grinds. But grinds that actually go somewhere and have purpose.
Virtually all of XIVs endgame is warp to arena kill boss done. There no structure to any of it. Every fight is completely segregated from everything else