Idk, I'm comfortable saying someone is "from here" if their family history goes back >1000 years. Likewise for people with much less history here, but I don't want to get into drawing lines in the sand. If we take your statement to its logical conclusion, nobody is from anywhere except wherever the primordial soup was (or maybe we all claim Africa, since it's the furthest we have traced it back). It's absurd.

That said, I absolutely agree that immigrants are the blood of the nation. You will find no stronger proponent than me for expanding immigration. My heritage goes back some 150-200 years, though my wife and SIL are immigrants, and I welcome anyone who wants to constructively contribute to come. I just think it's silly and honestly offensive to claim indigenous Americans are somehow immigrants as well.