Sure, it’s a big scale in most contexts, but not in the way that I mean here. It’s not big enough to cause the extermination of the group in question. Which is what matters in terms of whether it is genocide. It is certainly ethnic cleansing, human rights violations, mass murder, concentration camps, I think all of these labels fit

This is not a position that would be taken seriously by most scholars of genocide, including the man who coined the very term genocide, and would exclude the vast majority of genocides, including the Native American genocides, from the term. Ethnic cleansing itself is, by definition, genocide.

The atrocities done to the Native Americans constituted genocide because they were widely exterminated.

In the sense that you are using 'exterminated', no, they generally were not. Most Native polities were reduced by restriction of movement, impoverishment, and destruction of their way of life. All the massacres performed by white genocidaires in Native American history, horrific and repulsive as they are, are only a tiny percentage of the reduction and elimination of Native peoples in the vast majority of the USA.