"effectively conveying thought or feeling,"

I think this is present in military planning, and inferable from outcomes.

art is typically the creation of something new, rather than the destruction of something existing. One could argue that they are creating new corpses

That's not at all how it seems to me. There is a good deal of inferential distance here.

Supreme excellence consists in breaking the enemy's resistance without fighting.

In the practical art of war, the best thing of all is to take the enemy's country whole and intact; to shatter and destroy it is not so good.

There is no instance of a nation benefiting from prolonged warfare.

--Sun Tzu, translated

The art lies in reducing the number of corpses,etc.

we are talking about clustering and relative degrees of similarity

Excellent, yes! I agree that in English "art", unmodified, does not refer to war and should not be used to refer to war or a broader category of art of which one thinks war is a member. However, this is significantly due to historical use, rather than being the simplest stroke circumscribing a concept in concept-space. Excluding the art of war from "art" is somewhat like considering dolphins "fish".

I acknowledge there is some tugging involved, but what hasn't been shown to my satisfaction is that less tugging is involved for modern art, or other things generally considered art.