* Game about saving the planet.
* No world map, so you never see the planet.
Genius.
FF7's world map gives you a feel for the world as a whole that's greater than what you'd get from a simple static map screen, while also letting you traverse between locations efficiently. The field maps and battle backgrounds give you a sense of what the world of FF7 is like at human scale. Seeing the world on both scales is important to the game.
Open world games always feel like a small area to me, despite how much time they can take to traverse and regardless of how much stuff they have in them. Being at ground level the whole time fails to give you that global view. Add an airship and all you've done is make an inefficient world map. And I don't care to have stuff to do out in the wilderness. Sure, trade 5 kilos of Loco Weed to Choco-Billy for a Chocobo Lure materia, pffft.
Zones are not a compromise between a world map and an open world. Zones are, if anything, further away from a world map than an open world is and give you the least "sense of the whole" out of any alternative. As a replacement for a world map they have the same flaws as an open world, magnified. FF7 already had places suitable to "zone" type design. Mt. Corel, for example. Places you saw close up, but there were sometimes gaps between screens that got glossed over. That's the strength of the zone concept, being able to focus system resources to make a place look better than if you had to potentially display miles of terrain.
I don't believe that a world map is too expensive (though I don't recall if this argument was ever even made.) In order to try and meet the challenge of making a game as big and ambitious as FF7 on modern hardware Square-Enix has taken the (player-unfriendly) approach of splitting the game into separate parts. I don't believe there is any reason to let the world map slide on reasons of cost, they are already going to milk us multiple times so I'm simply demanding my money's worth. Fuck it, I demand more. The world of FF7 should be criss-crossed with highways, railways, and power lines, all that nature should be dotted with cell phone towers that allow the damn PHS to work. Drive home Shinra's impact on the environment.