Geomancers aren't crappy and !Terrain is kind of overpowered early on.
I can see how an entire party of them would be useless though.
Plus they're pretty useful for things like the Subsea Volcano where their ability to null damage terrain is actually relevant. Though yes, they suck by endgame and you can't even get their best weapon due to lacking a Thief to steal it.
Blue Mages are pretty useless without skills but since you'll be in them 24/7 you're bound to pick up a few spells and then you're just gimping yourself for the sake of gimping yourself. Plus they have a few decent choices for equips (roughly on par with Red Mages at least).
Berserkers, while one trick ponies, do that trick pretty well (they are pretty beefy at least). Too bad Monks basically outclass them completely before they even show up.
Ninjas are fucking blenders even without any sort of defense. If you want Ninjas but worse, take Thief instead (same lack of durability but obviously lacking in the killdozer department).
Dancers, even without all the gear, can still be pretty dodgy, and with four people you're bound to hit upon Sword Dance or Jitterbug sooner or later.
I'd put my money on Bare
frankly. All they have is unlimited equipment options, the ability to use items, and nothing else if you never leave it.
But honestly, if I really had to reclass them into something for the sake of the argument then Berserkers
. Better beatsticks are already available to you by the time you get them, their equipment sucks (Axes lose their novelty when FF style Knight Swords are around), and you can't fall back on the item command and the oh so broken option of chucking elemental rods at all your problems like everybody else can (including Bare).