For marketing reasons of course they don't want the Switch to be referred to as the Wii U successor because the Wii/Wii U brand became toxic.
But in other interviews, I believe Nintendo designers have just said straight up without the Wii U from a design perspective there would not be a Switch.
Even during the design of the Wii U, I believe Iwata said they wanted to put the hardware directly into the Game Pad (which would've made it essentially a Switch), but at that time (circa 2012) it was impossible to accomplish. The Wii U and Switch having the exact same screen size down to the millimeter also suggests probably NX/Switch prototypes started off originally in Wii U Game Pad casing.
Beyond there's no fucking way the Switch has anywhere near as strong of a year 1 without having Breath of the Wild, Mario Kart 8, and Splatoon 2 (a "new" game but many assets and even many stages full on taken from the Wii U game) in the first several months of release. Cannibalizing the Wii U software really helped the Switch get off to a strong start and it continues to help the Switch even to this day as they continue to plug droughts by porting more and more Wii U software (Pikmin 3 and probably Mario 3D World coming). If you remove BOTW + MK8 + Splatoon 2 + many other Wii U titles from the Switch, the sales are likely no where near as impressive.
If you remove the Wii U ports (BOTW, Mario Kart 8, NSMBU) or games moderately retooled from the Wii U (ie: Splatoon 2, Super Smash Bros. Ultimate, etc.), honestly the Switch probably would be in a bit of trouble.
People need to stop equating market success with a system being "good" or "bad".
Just going to put this in points because I find it easier to break down.
1. "without the Wii U from a design perspective there would not be a Switch." is not the opinion I got from reading articles about the Switch design history. Some did specify that the Wii U was an example of what not to do, which is something, but I don't dispute that, and do suggest that the Wii U is like a failed experiment.
2. "I believe Iwata said they wanted to put the hardware directly into the Game Pad" - Like a handheld? That's a different type of console than the Wii U. It also indicates that before they developed the Wii U, they were trying to make something more like the Switch. That also means that the negative example of the Wii U (as indicated in point 1) probably wasn't required, since Nintendo was already aiming for the Switch. That doesn't surprise me too much since the Switch does incorporate elements from the Gameboy all the way to the Wii and DS, but not the Wii U or 3DS.
3. I don't think copying the screen dimensions indicates anything other than that they really really like that screen dimension.
4. The games ported to the Switch from Wii U didn't require the Wii U to be developed. They could have easily debuted on the Switch or a Wii HD.
5. My post is about the marketing success of the Wii U, so calling it bad for its failure on the market is the point.
I describe myself as a little dose of toxic masculinity.