Black Tiger, I guess as far as length goes, it all boils down to how you measure the content and length of a game. Though not groundbreaking, going though dungeons, battles, finding items, characters, places, required or otherwise, is the very bread and butter of the gameplay of an rpg.
Besides, not all of such extra content is cut and dry, go from a to b and get the hidden thing. Many times it is broken up with clever dialog, riddles, puzzles, and/or events. You oversimplify it far to much. Besides I don't care for breakthroughs necessarily, just content that is fun.
Super Mario Rpg broke up the gameplay at several points in various subtle ways. The dialog for one was often simple but humorous. Seeing Mario reenact events was priceless. The things such as the the extra timed button presses in battles for more/less damage, the Yoshi racing, mode 7 mine cart ride, and that race up hill, amongst many other things, while very simple, provided a nice change of pace than the more serious rpgs. The great thing about Mario Rpg is it is just as much for rpg lovers as it is for everyone. Anyone can pick it up and play. Even though like most cart rpgs where a lot of graphics are reused, Mario rpg is one of the ones where you can barely tell as you play it is so well done.
Every dungeon and place, even those that use the same set of graphics, are done in such a way that you can't really tell much was reused as far as dungeon layout goes while you are playing. I can remember quite a few places in even Lunar SS where the room layouts were reused and stood out.(though by far it isn't as much as most cart rpgs). The people that don't enjoy Mario Rpg are usually the ones that expect too much from it, or something different than what it is. Maybe if it didn't have "RPG" in the title
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Your definition of "meaningful content" to me seems like meaningless extras like fmv and more sprite art, backgrounds, etc. Yes they are nice, and they can help make a mediocre rpg into an excellent one (and they can make an otherwise excellent rpg into a really crappy experience); however they are far from needed to make good content.
Admittedly I have played a small handful of pce rpgs, namely the us released ones. Though there are many more than just the falcom rpgs, for some reason I always associate pce rpgs with falcom, of which I have played some of there rpgs on other consoles/computers. Falcom rpgs are almost always very short. I disagree with being able to get anything about what's going on with the language barrier. Maybe if you partly understand what is being said, but for me I have always been highly annoyed when I don't know what the hell is happening...at all. No the fmvs don't help, in fact they only serve to confuse, and annoy me more. Having to refer to guides to get through a game is no way to play, it ruins the experience for me completely. Especially when hours are wasted trying to find that one last damn townsperson/place/thing you are supposed to talk to/examine to initiate an event, that is COMPLETELY unobvious when you can't understand Japanese. I spent 3+ hours slowly figuring out what to do in the first town in Magicoal (a game I thought would be obvious and easy enough to figure out). I finally hit a road block, and no matter who I talked to, what I examined, what I did, I could not figure it out. I turned it off highly frustrated, and have not played it since. Though stories of jrpgs are far from novel quality, when crap like that arises from the language barrier (and it happens A LOT) I don't see how anyone can find the game enjoyable, especially when they are turned based battle fest. Besides it's the characters that often make a jrpg, not the story.
I don't really count fmv as something that lengthens the game or gives much more meaningful content, in fact most of the time, I just skip fmvs if possible, especially in Jrpgs that are not translated. (I actually kinda hated fmv heavy rpgs and still do, well the copious use of fmv that is). Honestly when looking at the length of a game I personally don't count fmvs, unless they have vital info, which many times they don't (though admittedly, many times they do.) Honestly I'd rather it happen as it does in most cart rpgs than watch a short fmv clip. It leaves far more to interpretation. I like using my imagination thank you very much, especially when it comes to characters voices. Cd rpgs with their fancy cinematics and whatnot destroy almost any possible use of imagination when they use such things in events.
I think the problem here is you tend to value the more artsy part of games ie the aesthetics, and presentation, while i value more the characters, gameplay and clever dialog/events. I love what they do with limited resources (carts). Early cd rpgs, are often just cart games with lots of fmv and redbook audio. In fact if you took out the redbook audio (and replaced it with chip audio) and fmv and left everything else intact, many 16-bit era cd rpgs could have easily fit on some of the bigger sized carts of the time. Considering that at the time, when cds allowed for "virtually unlimited space to make a game" what we often got really wasn't that impressive. You say text heaviness artificially increased the length of cart games, I say fmvs artificially increased the length of cd games (though perhaps, not as much), and the redbook audio artificially increased the content. (Chip music > redbook audio any day of the week). I speak for 16-bit rpg games in general not just snes vs pce.
On a side note, pce is an excellent system and my all time favorite, however as far as rpgs go I can only really speak for the tg16, as I cannot play pce rpgs. Perhaps I should not have made my snes vs pce comparison, however the fact still stands lunar is far shorter than most rpgs of the time, which was really the only reason I even brought up the whole comparison.