In Final Fantasy VI, the Returners are the underground group that is struggling against the Evil Empire against the odds. Early on in the game, only Locke Cole is working for the Returners, but in the first half of the game, all of the major characters join in, even those such as Edgar Figaro who were supposedly working for the empire, and those such as Celes Chere, who actually were.
The Returners actually manage to topple the evil empire, but due to the expected plot twists in the game, their victory soon loses its relevance.
Final Fantasy VII had more disc space in one of its FMV then the size of the entire ROM of Final Fantasy VI. But it wasn't just technology that put Final Fantasy VII ahead. The rebel group in FFVII, Avalanche had a well developed ideology and reason behind their war against the Shin-ra; and also had their own moral complexities and personal issues for fighting. In Final Fantasy VI, all we know is that the Empire is evil (just because they are) and the Returners are good. And the Returners are all good, and they all look alike.
Of course, for a game released on the SNES, Final Fantasy VI's politics and sociology were works of postmodern scholarship, compared to what had come before.