> Video games are designed to be played interactively. Streaming a single playthrough via a non-interactive medium strikes me as transformative.

This is one of those areas where principles like “fair use” and “transformative use” don’t really matter, since we’re talking about YouTube de facto policy, not the law. If YouTube decides to honor the claims, then that’s what happens. And YouTube generally errs hard in the direction of rightsholders just to be safe.