The Wii U was essentially already dead by the time Mario Kart, Smash, Mario Maker, and Splatoon came out. If the Switch gets all of those games in its first year, in addition to BotW, Mario Odyssey, and maybe a Pokemon game, that will go a long way towards averting the Wii U's failure.
True. NSMBU didn't seem to have the effect they desired. Probably due to NSMB2 and SM3DL existing so 3DS owners maybe not having a reason to get the console.
So it took a year for 3D Mario to come out and then 1.5 years for Mario Kart. And then 2 for Smash.
If Switch manages to get Pokemon, it'll have a multiplat Zelda with obvious Switch focus as shown by sales splits, MK8D which may drive sales we'll see, Splatoon 2 which will be big, ARMS which is a wildcard, Pokemon which is fire, and Mario Odyssey which is huge.
Within 9 months.
The key things are Zelda doing to expectations, Pokemon existing, Mario doing expectations, Splatoon 2 likewise, MK8D doing well, and a game to do better than expectations (FE W, ARMs, etc)