I never said Final Fantasy must adhere to a specific standard, but if that is what you are taking out of my post, you clearly are reading too much into it.
Going on a fantastical adventure can be taken many ways, but setting and tone as well as the atmosphere greatly contribute to these factors.
Outside a few bits and pieces in the teasers and short trailers of FFXV, there is very little to go on, I would go so far to say that FFXV is very steampunk in it's design, not unlike Final Fantasy VI, with Steam powered fortresses and factories (The Empire and Vector for example, and even Figaro Castle being submersible)
FFX wasn't overly medieval in it's design, but it did have exotic locales. While not so extremely linear as XIII was, the game still managed to feel the world was large in scale and to go start from the southern most tip of Spira in the Baaj Ruins and working your way all the to the Northern Wastes of Zanarkand, it felt like a meaningful quest. There was an actual goal and destination in mind, it actually felt like a fantastical adventure.
We don't know how FFXV will be in this regard. While the game will be heavily character driven, Noctis and crew, hopefully it will also be involving in terms of exploration and world design. The quest is just as equally important then just the people you are controlling.
It's not so much the setting but way the game is presented. Final Fantasy in the earlier titles was as much as the quest than just the character focused narrative. Being more hands on with the lore and world around you, rather then needing to read a bunch of datalogs to fill in the blanks for yourself.