Most PSX games were only multidisc due to the massive amounts of FMVs used by them though. You can easily find single disc RPGs with just as much game content but lack FMVs (eg Legend of Mana, Tales of Phantasia), or the other extreme of really short RPGs with loads of FMVs causing it to become multidisc (eg Parasite Eve).

Besides, if the FFs you mentioned were to be remade for the PS2 or whatever, they'd probably use DVD instead so not as likely to need multiple discs, even if they improved the FMV quality