What you're all missing is that this concept doesn't work if Starfleet or the Federation is involved at all
. Otherwise it's not a story about independent settlers facing great odds. It's Yet Another Story about the Fleet and the Starship Fanwank and Captain Glorious Godfrey saving the benighted colonists from the evil guys in pancake make-up.
You're all trying to come up with a Federation/Starfleet/Sioux alien backstory when it is completely unnecessary for the concept to work. It's perfect if it's prospectors going out into the great unknown and meeting natives nobody
knows about and get in trouble with them. Then the settlers have a choice: stand and fight, run back to Fed space or call for help. If they call for help, then the Federation has to make a choice, and all I'm saying is, the Federation won't necessarily choose to help people who are essentially trespassing on somebody else's property...and it would be better from a dramatic standpoint if they didn't.