i think we all agree that at least Venom, Kain, and The Joker are epic villains(or anti-hero depending on the moment in question)
Final Fantasy in general has not had the best villains at any point in their history. Kefka and Sephiroth were perhaps the best that we got playing that series.
that's probably the main reason he's remembered at all to be honest. he wasn't THAT great, but most Final Fantasy villains fall extremely flat. i mean Kuja? great backstory, but characterization, imagery, everything else about him was poorly handled. Ultemecia? very boring. Seymore? he was a joke as a villain overall. even the original Garland/Chaos was a pretty poor excuse.