• Lack of extremely obvious automation. Trying to use chocobo porter with your chocobo out - I've taken the trouble to talk to the NPC, select chocobo porter, and then even selected a destination. There can be no doubt that I seriously, really, actually, want to use the chocobo porter. But I have to cancel the dialogue, dismiss my companion manually, then go through all that dialog again to re-select my destination.
  • Hiding the interface and disabling all hotbar keybinds during NPC dialog. Whatever happened to the "opening many windows and all operational at the same time" idea that Yoshi-P had bragged about ever since 2.0? Try to do a custom sort on the retainer.
  • Minimal customization options on combat text. I don't care about other people's damage numbers. I want to see my own.
  • Forced consolidation of UI elements. Enmity bars compiled into the party list most likely due to low spec systems. Buffs and debuffs in the same frame.
  • Lack of obvious customization options. Different party list layouts: e.g. a 4-wide layout with HP/MP/TP stacked vertically, expanding to a 4x2 grid for full parties. Buffs and debuffs in separate locations with separate orientation: e.g. buffs horizontal and debuffs vertical. Hotbar orientation options and layout (e.g. grid layout) for every hotbar.
  • Lack of obvious functionalities. Pinning the map/hunt marks/animus books so they don't disappear with ESC? Hiding the quest tracker but showing FATE and dungeon objectives?

I've said it before, and I'm gonna say it again. FFXIV UI is prehistoric. Devs may be proud of its efficiency and it may use really advanced algorithms and programming techniques, but its actual usability is far, far from satisfactory.