Well its not about instanced vs open world dungeons for me. There is no need for open world instances. Instanced dungeons can be also nice like it was in WoW(BRD, Sunken Temple, Mara, Kara etc.)
There was open world part called pre dungeon (yes, small part of maze before dungeon - which was sometimes more complex than dungeons here in FFXIV, and actual dungeon.

Anyway one thing which also I dont like about dungeons and raids here, its like there are no structures which ties corridors together. Like Alexander or Coil. Bam turn 1, Bam turn 2, Bam turn 3 ... and I dont even know how i reached turn 2 from turn 1. Do you remember Kahrazan from wow? A house you can explore. You acctually know how you reached boss. And it was not like ... loading screen ... bam .. you spawned in location with boss like in ffxiv nowadays.