I think that there are varying degrees of abstraction, and concepts can't be so clearly defined as either one or the other.
For instance, you may think that the concept "shirt" is pretty concrete, but it's actually pretty vague. It leaves alot up to the imagination, such as the color, size, and detail. Therefore, it falls into a level of abstraction.
However, if an object is directly experienced, it is conceptualized in a way that corresponds with itself more. If this is the case, then aren't cognitive functions more closely experienced than shirts, hats and ballgames? The only difference is that they can't be demonstrated in the same way because they are mental phenomena and intangible.
(I'm toying with words here, actually. Concepts aren't concrete. So this conversation is about whether functions are mere concepts, which I don't think they are )