I still need to look over the second link you gave - sorry, am on mobile and switching back and forth is a pain

Ethnicity is just more specific. It's like saying gender and cisgender are the same when one is more of an umbrella term. I can be a white or black American, but I'm still American.

If you put an Italian next to a Swede, you'd likely be able to tell which is which.

This does not make sense to me. I would not know that if you put two random people in front of me and asked their country or ethnicity. To say otherwise I think pigeonholes that modern worldview and in a way minimizes the effects that racism has had uniquely to the 20th century. It's xenophobic to imply a regions culture is the cause of poverty but another level to say genetics are the cause (or both).

Would it be more accurate in your view if I distinguished instead by describing today's modern racism as being born from "scientific racism"/eugenics? I'm having a brain fart and feel like I'm forgetting a better term for that, though