To be fair, this isn't a problem solely with Bravely Default. I don't really enjoy any RPG where you have four identical characters (battle-wise) to mold into anything of your choosing. Making any decision immediately feels arbitrary, informed only by my knowledge and expectations from other RPGs, to the point that I may as well make a decision based instead on which costume looks good (which might be the design intention). And with job systems in general, there are two mirrored constants, and everybody could (and will, given time enough) end up where they started: as four identical characters once again. So there's zero motivation to see what's next. Of course, there's no plot in the demo, but I very much doubt that plot carries this game, and at Level 10 it already feels like a grindy slog where my interest is only held by the item descriptions, and by the knowledge that playing it at night will result in me more easily falling asleep.
Am I missing something?
I guess it depends on how you look at it. Technically, yes, any character can become anything, and they can all master all jobs, if you actually wanted to put in the time and effort to do that. But it's a lot of extra work; in the demo, there are very few jobs with very few skills to learn so it's easier, but in the main game, you're not going to get everyone mastering every job without doing some very excessive grinding, and given that all characters should ideally be filling different roles in the group, as Bardull said, leveling them up in jobs they'll never use seems pointless.
But to say they're identical at the beginning isn't exactly right, as they all have very slight natural tendencies toward certain stats: Ringabel favors speed and evasion, Edea's tanky, Agnes is all about magic and Tiz is balanced in pretty much everything but has the highest base HP, which makes compartmentalizing pretty easy. Early on, I basically just locked each character into an archetype and distributed jobs accordingly, sometimes deviating if I found there was a skill for one one of the jobs that would benefit a character I wasn't planning on promoting that way initially (I remember finding in the demo that the Turn Tables ability from the Red Mage class was a terrific fit for the Ninja).
So the fun for me mainly came in the discovery of what certain jobs could do for my characters in unexpected ways, and how jobs I had already leveled quite a bit aided ones I would get later. For example, the Arcanist, a role you get relatively late, basically exists to be paired with the Black Mage, a role you get very early. So by the time you've just about done all you can with the Black Mage, you have a new role to switch them to and continue using everything they've already learned.
True enough that the story isn't what carries the game, and the characters aren't the best the genre has to offer. Edea's great, and Ringabel is almost great, but Tiz is a bore and Agnes is about the most annoying she could possibly be. So if that's what mainly draws you to RPGs, it may not scratch the itch. But for anyone who enjoys the item management and character growth aspects, Bravely Default's kind of a dream come true. Or at least the first half is.
