I disagree strongly.
Squaresoft was already well known for having top-notch graphic and sound design all through the 16-bit era. All the FF games, Seiken Densetsu 2 and 3, the Romancing Saga games, Chrono Trigger, Bahamut Lagoon, Front Mission, just to name a few.
FFVI was the first SNES game to use all of the systems 256 color capabilities, which was a graphic marvel at the time.
I can still remember looking in GameFan in early '94 and being absolutely floored when I saw stills of FFVI.
Compare Sega's Phantasy Star IV to Square's Final Fantasy VI. They came out within 4 months of each other (in Japan, at least)
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The amount of colors, texture work, character models (and animation, albeit simple), and effects outclassed any other console RPG at the time- and stood pretty damn well against non-RPGs, too.