And what gauruntee do you have that a "Switch 2" doesn't have the right design and doesn't have marketing missteps. Zero. The Wii U's failure really was more rooted in consumers growing tired of mini-game-athons that drove Wii to super high sales, you release Nintendo Land 3 years earlier and it sells 20 million, three years later you get treated like crap. Consumers are fickle, you can't bank your company on every console transition going well, Nintendo fails about 50% of the time when they've had hardware transitions.
It wouldn't have to be 3 years of support either, it would be more like 5-6 years of support, there would still be hundreds if not thousands of games compatible with the OG Switch and probably all of the important Nintendo 1st party games can scale very easily because Nintendo doesn't really aim for realism in their presentation, so it would be straight forward to have say Breath of the Wild 2 (hypothetical) run at 60 fps 1440p (4KTV) on Switch Pro docked versus say 720p on the OG Switch.
See I wouldn't have a problem with this concept if I had any faith that the base Switch would still be properly supported after the release of the Pro/1.5, but I have no such faith.
Nintendo will still make sure their games run fine on it, sure, but non-Nintendo releases will end up like Hyrule Warriors on the base 3DS chugging along at 20fps.