If games are art, which they self evidently are, it is because of game design and game play. If you only see games as a wrapper or delivery vehicle for narrative, visuals, or music, I think you fundamentally do not respect games as an art form. What a tiresome discussion.
Like stuff that's almost entirely gameplay focused and fits into a specific single player or co-op genre, that's toys. Multiplayer games that are mostly about competing against someone else, that's sports. Story driven or more esoteric games, that's art. Do you get what I mean?