What counts is the utility of the word.

To have a special word makes only sense if its content is distinct from the content of an alternative word.

The challenges faced by a modern corps commander or his WW2 equivalent, an army commander, are different than the challenges faced by a brigade commander.
Logistics play a greater role, fixed values become variables (such as through the ability to influence the theatre air war), geography and time are to be considered on another level. An army commander concerns himself with the question where to cross a river and what to do next, while a brigade commander is concerned with how to cross the river and how to get his folks over it in time to proceed.

You cannot expect much success if you take the classic tactics of a battalion and simply interpolate to Corps level. You need different stuff, and said different stuff should be identified with a different term.

I don't care much whether you call it "grand tactics", "operational art" or differently, but "operational art" happens to be the widespread term for it and this makes it first choice for communication. The choice has been made already, so there's little to gain by discussing language since the differences warrant a different term as laid out before.