While US settlers were not of the professional-managerial cohort and did not find high-end work, they were awarded private property for exploitation and investment.

More specifically, as I've consistently mentioned, they were bought off with land. This has several qualities of various classes. There is a rentier quality to owning land, you can make money with no production, so not as private property. It can be used for production as well and this is what many settlers did, using the land to become farmers, ranchers, and small-time miners (though much of that was later acquired by bigger fish). Though owning private property does not fully determine one's class relation, as we can stick a sole proprietor into that category as well as "yeomen farmers", people who mostly work their own land for subsistence. Making and selling commodities oneself under capitalism is a petty bourgeois activity. Consuming your own product for subsistence can be seen either as a byproduct of this or as an older form of subsistence farming that would make you a special case under some forms of feudalism. Individual farms often had both characters, with a productive farm for market and a set of beds to feed oneself. And then there were settlers that took land and sold it, attempting to be speculators, more or less financial speculators operating at different levels.

Though this is the settlers that directly stole land. Western expansion also included workers who received different amounts of settler status treatment. The miners weren't all owner proprietors! Nor the farmers. Workers were employed and were also bought off by the rising tide of buying people off with land. It was predominantly black and Chinese workers that built out the railroads but they received the treatment of the marginalized. Nevertheless they would frequently buttress the settler system, taking on essential roles for violent genocide in part because it meant better compensation. Were they still working class? Irish and German immigrants came in waves to become both settlers and workers, dying in mines for capitalists on one hand while enjoying the privileges of white settler culture on the other. Some of the most racist, anti-worker working class operatives were from these groups, white-ified for ruling class interests. Were they working class? They were certainly settlers.

It was, in fact, in the class interests of settlers in the US to participate in genocide - and that's exactly what they did. I do not think you're giving the settler-colonial situation enough.

I mean, I said basically that exact same thing in my previous comments, I just don't use the term class interests because this is an example of false consciousness that is the usual bargain for marginalization under capitalism: a subset of the working class gets bought off with an increase if status, but will still not resolve the class conflict overall, not even within the group that is bought off, as capitalism will still dispossess them. Western expansion kicked this can down the road, as it created an external front for initial disposession by the small-fry settlers (built in genocide of the people already there). But the capitalists still encroached rapidly, stripping most those settlers of their newly-acquired petty bourgeois traits. This inevitable clawing back coincided (not coincidentally!) with the rise of labor organizing. But even with land owners as a small and decreasing minority in the west, settler culture remained and was combined with other means of creating marginalized and non-marginalized groups to serve ruling class interests. It is part of the same continuum.

The national liberation struggle is different in different contexts: settler-colonialism, segregation/apartheid, caste, internal colonization of migrant labor (I'd also point to the use of undocumented labor as a similar dynamic in the US), these are all class structures which change the class dynamics by inducing different relations to the means of production.

Basically every serious South Asian Marxist will tell you, at length, how caste is not simply a class relation. There is a danger in assigning too many social relations directly to class relations, as one can actually grab onto what seems like a primary relation to production when it is actually a secondary effect of a different, primary relation to production and a consequence specific to historical material development.

I do agree that every example you list is a real form of marginalization that is maintained by (and often created by) ruling class interests, I just disagree that they are simply classes on their own, let alone one's primary class relation. I say this in part because, of course, every individual actually has the aspects of several classes, and so do various ways we can group people. This has always been the Marxist understanding of class. The working class will have bourgeois qualities, for example, and this is part of the core dialectical framing. Trade unions are frequently petty bourgeois as all hell, will be openly imperialist, racist, xenophobic, demonizing of the American working underclass you mention, etc. Even the trade unions made up entirely of the working class. Even if you kick out the "union bosses", the contradictions remain in that working class organ of power.