If it's different, then its not a dynamis type fight. Dynamis wasnt fun, it was repetitive, it was mostly farming trash mobs, it wasnt an 'open ended dungeon' it was just a recycled existing zone with boring mob placement compared to the rest of the game. Even the bosses weren't that interesting, most of them were just stronger versions of the normal mobs, or they had like one special mechanic you had to be aware of.
The 'a lot of people working together' wasn't even that either. It was just a bunch of bodies spamming their strongest spell, or swinging until they got the tp to use their strongest weapon skill, or the thief just swinging at stuff for treasure hunter. The fights in XIV at least DO require people to work together for the mechanics, and the reason we dont have large scale content like that is because, quite simply, people wouldnt be able to work together like the way people seemed to think it was in XI. CT is proof of that. The only reason most people ever did dynamis in XI was for the gear years later because the way that game functioned, every new piece of gear was such a small upgrade that we were still using lvl 50 gear at 75, and years after it was first implemented, just so we could switch it in for 2 seconds in a macro.
It's nostalgia, it wasnt fun. I enjoyed it during its time but no, going back to that isnt the way. By all means make suggestions for large scale open dungeons, but dont compare it to old, grindy, dated content from a game that was released a decade ago.
Dynamis only became fun after the changes that took away the zone reservations and you DIDN'T have to follow a one way predictable path or take in a huge group of people you didnt necessarily even like. Despite it being a wide open zone, thats what everyone did, they followed the same path every week because it was the most profitable/they needed to take out certain bosses and work their way through. Anything 'open' about it was just an illusion.