You really should not dismiss the concept of a sandbox MMO design out of hand. Methinks you've had a bad experience in playing EVE Online. (Note: I consider EVE to be a "Macro Sandbox" - that is, a sandbox for the bigger people who run alliances, etc...but it's not as sandboxy for the average player)
Have you ever played Star Wars Galaxies? I mean, have you explored its features that makes it sandbox? You have a tremendous amount of control over your own assets in the game, and that is what made it so appealing to me. You could set up ANYTHING outdoors - resource extractors, houses, factories, even military bases and entire cities, along with the ability to set up props like tents, camps, even ships and other fixtures. You also had the ability to create and program your own NPCs in SWG, for when you wanted to host an event. (They were called Storyteller NPCs) You also had a higher degree of control over your character's identity, and how you developed that identity.
In SWG, I was a smuggler/pistoleer who was also once a city mayor, and also operated a cantina or two. I also often butted heads with Imperial players, raiding their PvP bases and blowing them up. I dictated what I wanted to look like, and had complete control over my appearance - I could be fat, thin, snappy-dressed with fancy clothes, or look like a total street bum; the same applied to weapons, I could buy a standard weapon, or get it tricked out with a scope, different stock, or other features that made it look drastically different from its original version. (The Han Solo Special DL-44 was my favorite.)
Again, don't dismiss sandbox MMOs out of hand - they are extremely flexible gameplay systems that work great for a variety of purposes. I'm not saying we should have the option to build our own cities or houses out in the FFXIV world, but rather have similar levels of control over our game experience. The very definition of a Sandbox MMO is this: Your game experience is yours to control, from top to bottom, from the surface to the depths of the game - every aspect of the game, you could influence in one way or another.
It's that simple. Sandbox MMOs: You control your entire game experience.