Here is an image showing how "race realists" and "anti-race realists" view human biological variation:
The first shows a genetic continua, with relatively abrupt, or sharp breaks between local populations. The second agrees with the first, but adds sharp breaks between each continent (groups of populations as races) and imposes a hierarchical clustering, e.g. each local population falling into a much larger regional grouping (race).
I would consider myself to be a race realist and yet my races can be cut from a continuum. Steve Sailer and Michael Levin, two other self-described realists, allow for the same. Obviously different meanings of "realism" are afloat. For clarity, we can simply call your type "Krom-race realism". I have already noted my problems with this:
1) Historically intraspecific races were not thought this way. Discontinuities evidenced species, continuities races.
2) Presently, many self-proclaimed "race realists" do not have a problem with continuities.
3) Presently, taxa subspecies can be cut from continua.
You add another:
I don't really like the term "race realism" because it implies an ontological position. Instead the race dispute in biology is whether race as a concept is an accurate or productive (useful) way to describe/capture human biological variation, not whether race "exists" or is "real".
I actually employ "realism" in an ontological sense. You do not. What I mean is that "the concept references something in nature". What you mean is that "that which is referenced, at least when it comes to humans, is worth my attention".
Maybe you should call "Krom-race realism" something else. Do you at least apply the formulation consistently? If climatic zones run seamlessly into one another are they not real. Are clines (i.e., character gradients) by definition also not real? Or do races alone need to show "abrupt, or sharp" breaks to be "real"? Why?
This is philosophy not science. The debate about race and 'natural kinds' has no relevance to biology.
I don't care for the "nature kind" nonsense either. It adds no clarity to the discussion. The concept of "natural division", however, does -- since the distinction between natural and artificial division is pretty clear and well understood in biology.
Can you show anything exists?
Yes, if you define "exists" in a way that allows you to show this. I do this in my section I. By this ontology, for example, dinosaurs don't exist because while the concept is biologically coherent no referent is currently to be found.