You can make VII like that too, it's just up to you who has the steal materia, who has enemy skill and who has slash-all or whatever.
That's the problem. Every single character can do everything. In FF6, you have to make do with what you have. You can't just laugh and switch the skills to whoever you want.
You'd think so, but more options really take away from the strategy because it doesn't limit you as much. Since every character can do EVERYTHING you want them to do, it doesn't take as much effort to stay alive. It lets you turn them into gods.
FF4 leaves you with the disadvantage of not everyone being able to cure and not everyone being able to attack. Each character has strengths and weaknesses. Sometimes you won't even have a white mage or black mage in your party. Or they'll run out of MP or die and then you'll be screwed. One character will have to use a life potion if you have any and another will have to use a cure potion if you have any and maybe another. Then you have to think about if you should even use a turn to use life since they might kill her as soon as she comes back when you could be curing somebody else or attacking. For FF6/FF7, all you do is use life2 with anybody. If a monster is weak against fire, well use Fire for everybody! You don't have to worry about silly things like fire and ice weapons.
Like someone else said, they could have easily made it where Barret's cure magic was much less effective than Aeris's, and Barret could have had strong weapon skills that Aeris would've been able to use. And someone could have had strong attack magic that no one else could use. Everyone shouldn't be able to use the best spells. Just so they would all be different and useful. It doesn't make a tiny bit of difference if you stick with the same three characters the entire game because they're all identical. Where's the strategy in that?