Abstract concrete distinction: a matter of degree?

In previous posts, I talked about how some abstract objects may have concrete components. Many philosophers seem to think that this abstract/concrete divide is black and white, that all things are either abstract objects or concrete and nothing in between. Either objects are like numbers/pure sets or they are like rocks, planets, chairs, etc.

But many things in reality are not so clear cut and what do we even mean by abstract anyway? It's kind of like a definition of god, negative definitions abound. But there seems to be many criteria for abstracthood. Satisfying some but not all may at least intuitively deem some objects partially abstract or partially concrete. I've identified several criteria and given examples of objects that satisfy them but not others.

Observability: I take this to mean something like cannot be seen, touched, smelled, tasted, heard, etc. Some objects cannot be observed in these ways. Electrons are not observable even in principle as the laws of optics prevent us from seeing them; they are just too small. But electrons also has some mass and thus many people, common folk as well as philosopher would not think to attribute abstracthood to electrons and this leads me to the next criteria.

Mass: Some objects contain no mass such as photons. But photons have other properties like linear momentum and occupy space and has causal properties and thus many people may not attribute abstracthood here either.

Spatial extension: Some things lack spatial extension such as the geometrical center of mass of the planet earth. They are merely points in space(time). But in some sense, this is also not an abstract object because it is not causally inert. It exerts physical effects on the world. Our equations for properties like centripetal force rely on this object's existence (if only as an abstraction!) to work.

Non-gerrymandered: Consider a chair. No one doubts that this is a concrete object (except maybe ontological nihilists or those like Van Inwagen). But what about the mereological object composed of the chair and the table (chair-table)? This object, if it exists, seems somehow unnatural. It is a gerrymandered object. It does not "carve nature at its joints." It is not a natural kind.

Causally inert: Only the most abstract of objects has this last property and this property may be the most weighted property of abstracthood. Numbers and pure sets have it. Maybe some other things have them as well (the Good, etc). Causally inert objects do not cause things to do this or that. They just are, they exist in some abstract realm. If it has this property it has the others as well.

What if an object as some of these properties but not others? Some are probably weighted more than others but i will not advance any kind of quantitative or qualitative weighting myself. But it seems to be reasonable that satisfaction of some of these properties may be at least somewhat indicative of abstracthood especially if it satisfies several.