Updated in bold. Many people tried to defend the Wii U in this thread, by mentioning all the 3rd party ports for the Wii U. But at this point I think it's safe to say that Switch is getting just as much 3rd party support if not more.
Switch gets the following games within ten months of launch.
A massive open world Zelda game.
A Mario Kart Game
An Online Third Person Shooter
A huge ambitious Mario game in the vien of Galaxy/Sunshine
A successful crossover game with Ubisoft.
A good fighting game (Pokken DX Meta is at 80 now).
A portable version of Minecraft.
A portable version of Skyrim.
A portable version of Doom.
A sequel to an RPG that American fans begged Nintendo to release over here.
Portable versions of many Indie games.
Meanwhile what did the Wii U have at this point? New Super Mario Bros U, which many fans thought was paint by numbers, and a port of a MH game that was already on two other systems, and Pikmin 3.
It's like Nintendo is hitting all the right notes with their software library for the Switch right out of the gate. Most of these games have huge potential to move units.