I agree that a term to indicate "that group whose families have comprised the population for generations" can be useful and indiginous will do as well as any.   The only problem is - how many generations and what counts. In my own case, my mother came from Co Limerick when it was still part of the UK. You may think that is obviously British (or indeed obviously not.) My fathers' side had all lived in England for at least 5 generations, but before that they didn't as far as I have been able to trace. I reckon you will find most British people (defined here as 'allowed to hold a full British passport' *grin*) have an ancestry that is a complex or even more so.