They aren't accurate.
At least about the 2 GB mark.
It's been said - and I don't have much reason to doubt this - that Final Fantasy VII's game data is essentially the same on all three discs, with the biggest and possibly only difference being the FMVs which take a lot of space.
When I borrowed a PSX to play FF VII, I confirmed this with a particular trick - during game play, at some idle point where the disc isn't being loaded, like when you're standing around, you can safely swap discs. You'll be able to play the game normally even when another FF VII disc is in there, but when you hit a point where an FMV cutscene would play, you'd instead see a different scene.
Maybe it still would be about a GB, but I doubt all three discs are full up to the max to be approaching two.
Through some optimizations and compressions and whatnot, it's been speculated that FF VII could indeed fit on other formats such as a single DS card. But for downloading, if it takes a minute to download 200 kB, it will still take a long time to download FF VII, whether it's one CD or three, whether it's several MBs or a GB or two. If it could download in the background while you do other stuff, then it would be okay. And directly to an SD card would be nice.