Honestly, the OP wasn't entirely wrong. I've noticed that its common for Nintendo systems to sell like crazy during launch period no matter how unsuccessful the console would end up being, it didn't only happen for the Wii U. The Gamecube and N64 when they launched had huge console sales during its launch period but both systems would end up selling underwhelmingly.
The reason behind this is obvious, the fans who buy the system during the launch period are far from representative of the market you need to attract to make your game system successful, which is the more casual market who doesn't wait til midnight to pre-order a console or go on forums debating about console sales. The time period that really proved when a Nintendo system is successful or not is post launch period once the hardcore gamers got their system and now they're attempting to get the more casual gamers, the Gamecube, Wii U, and N64 did great at capturing the more hardcore fanbase at launch but failed to be appealing enough in the long run to appeal to the more casual gamers.
However, for Switch 2 I highly doubt you need to even wait post launch to see if it'll do successful. This launch is projected to far exceed any other console launch Nintendo has ever had and its not even close, Switch 2 launch projections expect the system to sell between 6-8 Million in its first 3 days, over HALF of the Wii U's lifetime sales in its first weekend and it took the Switch 1 a few months to even reach 6 Million, it'll be hard to picture a console doing underwhelming after having a crazy start like Switch 2 is expected to have.