I think y'all are under estimating the selling power of just Zelda, Splatoon 2 and Odyssey. On top of that, which is just first year, we are getting Pokémon as well, as already confirmed by Gamefreak. Now, Pokémon, Splatoon, 3D Mario that has the selling potential of Galaxy and Pokémon. That right there already screams over 20m. Not to mention the inevitable smash bros, hopefully it gets Monster Hunter... plus, Nintendo still can pump out Animal Crossing as well as a bunch of other IPs that will help the console.
I really don't think you should be judging lifetime sales based off of the launch lineup. Whereas yes it's pretty weak, the first year is pretty strong.