I have not owned a Wii U or a Switch, but these are my thoughts.
Long term plan did seem to show that the Switch was going to become the eventual successor to the 3DS.
I think the Wii U is a superior feature-rich machine vs the Switch as it allows you to view different content on the handheld controller and on the big screen allowing for maps etc and a more immersive experience. I don't need to play games on the go.
Zelda Breath of the Wild was designed for the Wii U but the map on the controller was taken out, it was reported, so it wouldn't outshine the Switch version on features.
Opinion:
The Switch is good, but it doesn't do 3D like the 3DS does and it doesn't do multi screen playing like the Wii U OR the 3DS does. The joycons are much cheaper in feel compared to the Wii U's controls, and the symetrical layout of the Wii U's analogue joysticks is superior to the asymetrical layout that the Switch uses.
I am a bit disappointed that the Switch Lite has come out, as it almost ensures that the original Switch will not be coming down in price soon (if ever). I would have rather had a $250 Switch instead of a $199 Lite and the $299 full. The Wii U was never discounted in prices from $299 to my recollection. Only the GameCube I believe may have ever been discounted amount Nintendo systems, other than Nintendo bringing out the 2nd versions of the NES and SuperNES.