Honestly, it is only enthusiasts who care about parity anyway. The average consumer wants something different from what they can get on the platforms they already have. I am an enthusiast who understands this. I already have a PC and probably a PS4 in the near future for third party multiplats. The reason why I bought a Gamecube, Wii, and Wii U was because they provide me with unique games and experiences I can't get anywhere else. No platform can be everything for everyone.
The Switch will be a platform that will likely get a lot of indie middle-ware, AAA, and all types of games in between. It is the platform that will allow developers to experiment with new ideas without having to compete with AAA standards. It is a platform that will allow Nintendo to focus on making great experiences by focusing their efforts and talent rather than dispersing it across two different platforms.
It will sell because it will have Dragon Quest, Monster Hunter, Shin Megami Tensei, Mario, Zelda, hopefully Metroid, hopefully Xenoblade Chronicles, Super Smash Bros, Pokemon, Animal Crossing, Mario Kart, Fire Emblem, Splatoon, Japanese middle-ware RPGs, a small assortment of Western AAA games, and a multitude of other popular titles that one can play at home or on the go. The problem with the Wii U wasn't that it only had first party titles, but rather that it did not have *enough* first party titles to make up for the absence of third party. The Switch won't have this problem because it will likely have Japanese third party support, and Nintendo can cohere their efforts to a single platform.