I don't see a problem with them charging for post launch content, even with the announcement pre-launch, the game sounds feature complete (difficulty settings haven't typically been a feature of Zelda games) and no doubt you're going to get a full experience.
Hard mode is the only thing that would concern me, unless they are having to significantly alter the game post launch I don't really see why that should be behind a pay wall.
Also not selling items/content individually is not a great practice, especially as you don't know fully what you're going to be getting.
Don't ruin the moment
Currently Playing: Rocket League (PC/PS4), Dead Cells (PC)