rearnakedwindow I actually didn’t know that FF2 was a success in its day, so that was cool to learn, too.
It was successful in general terms but not especially successful relatively to the rest of the series—it did a little better than the original in Japan, but the original also got a US release that pushed the total sales much higher (it actually sold a little better in the US, iirc), and then sales exploded with FFIII to the point where it outsold the worldwide release of OG FF without ever leaving Japan. Even afterwards, FFII’s ports and remakes were almost always bundled with OG FF, so it could never bridge the gap (plus they generally change the game so drastically that you have to wonder if they’re really the same game anymore).
The SaGa series has a perception of being a second-tier series in the Square hierarchy but it was neck-and-neck with FF for a while—the very first SaGa on Game Boy was Square’s first million-seller, for example—but FF got even bigger at the tail-end of the SNES/SFC, and then FFVII obviously made it untouchable.
Part of what held SaGa back forever is that it couldn’t really scale up in budget/scope the way FF and other series could, nor were the developers especially interested in the graphical arms race, but we’ve reached a point where people are less likely to dismiss or pigeonhole games based on how they look, which lets SaGa games compete on their own terms and not have to worry about selling twenty million copies or whatever.