I have to say that Bender from Futurama
best sums up my feelings towards the Ba'ku:
Oh, cruel fate, to be thusly boned. Ask not for whom the bone bones. It bones for thee.
Does it suck for the Ba'ku? Yes. But instead of expelling the S'ona in the first place they maybe could have come up with a way to integrate their need for exploration into their society. Maybe be a little more forward looking so they could defend their paradise when someone inevitably stumbled upon it.
Except we don't really know much about how the split happened except that the Son'a tried to take over they and then they were exiled.
Heck even the how could the Son'a lose to luddites argument only works if you believe that the Son'a who were apart of said luddite village some how got access to advanced technology that their parents who ran the colony didn't like having around.