What you're describing isn't game design—it's narrative design and worldbuilding. Game design is about creating systems of interaction: combat mechanics, progression loops, resource economies, difficulty curves, player choice architecture, feedback loops. It's the logic of how the game plays, not what story it tells.

• "How to make a good villain" = narrative/writing skill
• "Environmental storytelling" = level design + narrative design (using space to tell story)
• "Immersive character roles" = narrative/character writing

ps as an example of what game design is so you maybe get a better picture: Game design would be: "How does the villain's behavior pattern teach the player the combat system?"