Presumably they have something relevant to do in this era? That's an odd stance, it's like saying what's the point in Bronwyn or Disa if her descendants aren't in LOTR.If the Harfoots aren't precursors to the Shire hobbits I'm not sure what the purpose is in having them on screen at all.
Not seeing how this makes a difference.We might see is a change in leadership over the seasons of the series, where Harfoot leadership is adopted by critical members of the community and usher a small but steady change that as audience members we can interprete as the beginnings of a sedentary, less superstitious Hobbit culture.