I'm not going to lie and say that there isn't anything wrong with FFVI (Thasama REALLY needed to be located closer to the middle of the WoB rather than at the tail end of it) but for the most part its lack of a definitive main character really helps it out (by which I mean nobody's permanently welded into the party leader position like in there is in most JRPGs; probably to try to hide the fact that the 'main' character is a grrl which continues to be an incredibly rare occurrence, especially when not treated in a derogatory manner ala Neptunia and the like). Instead you basically have free reign over your party load out for most of the game (outside of events where everybody's scattered across the globe) so if you got tired of Terra's pursuit to understand the virtues of becoming the perfect Japanese housewife you could dump her ass and spend some time hanging with Mr. 'Suplexed A Motherfucking Train' Sabin, Mr. 'Imagine Me Breaking This Game Over My Knee. Forever' Edgar, Mr. 'Oh I'm Sorry. Were You Wearing That?' Locke, and Mr. 'Thou' Cyan.
Strange, I always thought Celes was the main character. Well, I guess that's the beauty of it, it's one of the few, if only, RPGs that's definitely a full cast story. Final Fantasy games often have very strong central casts though: FF7, FF9, FFX, and FFXII all have some ambiguity over the lead, even if they feature an iconic young male hero. But FF6 is the only one where it's completely ambiguous.
Really, the only claim Terra has to being lead is the fact that the game begins with her. From there, she becomes part of the team. As the game progresses, she becomes more distant, and leaves for hours at a time. It becomes more "about her" then "from her perspective", while others take the reigns. Locke always remains a strong second, but always second, and second to who? For the middle third, it felt like Celes took over for Terra (which has some out-of-game significance, since they were originally the same character during development). Then, in the second half, it's COMPLETELY thrust into Celes' hands, while Terra & Locke are the dead last characters to rejoin the party.
As for Terra's story, I rather liked what they did. They originally set her up as some sort of romanic lead, being female alongside a male hero, and questioning her ability to love. But they did a 180 and instead of going for the easy romantic epiphany, she learns to "love" a group of children that she cares for. I thought that was pretty big of them. Actually, kinda opposite of the "perfect Japanese housewife"... it's closer to her becoming a nun. There's a slight hint of romance between Locke and Celes, and maybe a tinge between Edgar and Terra, by virtue of him being a horny bastard, but any romance tends to hinge more around exploring the characters' troubled past than trying to create some titillating love train. By the end, you see Locke as a broken, but recovering character who has a long way to go before any thought of romance is even possible. Characters are left happy, but the ending doesn't bring everyone together or set them up for "happily ever after".
My god, what a perfect game.