Quick is quite possibly the most obscure thing to find in FF6 (far moreso than Gogo or the Illumina certainly) so yeah. There are hints but even knowing that something was up, I know I had to just screw around in the Ancient Castle for a good long time before blundering across it. Moogle Charm I thought was easy to find - that's a noticeably weird place that I thought might contain something interesting or a stairwell, and definitely found it on my first playthrough (in which I also WoR-recruited Mog). Even if you want to throw out the Gem Box and the Fanatic's Tower as optional, sure, it doesn't make THAT big a difference. The biggest difference is definitely whether you recruit Locke and get the Phoenix Cave cool stuff, probably. Phoenix + either Ultima or the Illumina is a pretty huge boost in power. And when you get major clues to go find Locke and those locked doors in Narshe taunting you, it would feel odd to say that you're expected to fight Kefka without having recovered Locke. That feels like a maingame plot task. This is unlike SH2, where a bunch of stuff randomly unlocks after you've already entered the final dungeon with no prompt, or FF7, where there's no speech from Cloud about how before we settle things with Sephiroth, let's go raise chocobos and compete at the Battle Arena.
Incidentally, I agree about the Calmness hype, just that the best 7-8 characters in your party should be a mix of mages + people who can do even better than that. So yeah, the effect of any one character is reduced, but there's still a lot of broken to go around.
