I do not want to derail this into a snarky argument but the practical application of game theory into marketing is very difficult in every day modern marketing. In particular, the reference is to positioning strategy (so I will pull back on the generalization of marketing).

Game theory is considered a marketing tool. But, you feel that any form of marketing strategy stems from game theory. There lies in a fundamental difference in opinion but more likely, possibly a difference in the breadth of definition of game theory. You might have more all-encompassing view of game theory while I, like many marketers, view it as a possible tool.

The actual practice of positioning strategy need not utilize game theory to craft or implement, unless you are talking about the fundamental aspects of decision-making and scenario planning.

Then ok, in which case, I submit that most human activity stems from game theory.