Yeah it's a challenge play where you are limited to just four jobs. But you don't pick for yourself - Gilgabot picks for you. A "standard" run is one job per crystal, and you typically wait until you reach each crystal before revealing your job for that crystal. It's more fun with a bit of surprise. And there are other variants that change up the job pools (completely random, popular jobs, only magic casting jobs, only melee jobs, etc). I picked the Classic Jobs restriction (some combo of Knight, Monk, Thief, Black/White/Red Mage) for my latest run.
I really like playing FF5 with the goofier jobs. I have a real soft spot for Geomancer and Dancer - gotta love that randomness. But then it's also fun when you roll one of the game-breaking jobs that just makes everything easy. There truly isn't a four job combo that won't work.