I don't understand your point about levels of abstraction.

Imagine if someone said "This shape is not a rectangle. It is a quadrilateral." You would probably think, "Well, some quadrilaterals are rectangles, so the shape being a quadrilateral does not mean it is not a rectangle." "Quadrilateral" represents a higher level of abstraction than "rectangle" in that it specifies the shape less. Generally, the fact that something is accurately described in a vague manner does not mean it cannot also be accurately described in a more precise manner.

That evolution selects for the most reproductively fit is tautological, it is practically the definition of "reproductively fit". The reason this tautology is useful is that it gets us to ask the question: what more concrete properties must an organism have to be reproductively fit? Here the property of "tameness" has been proposed as such a property, and represents a lower level of abstraction. Though, not much lower, you correctly point out that "Evidence would require a clear definition of tame".