I have both copies and to be honest, the negatives that apply to the Wii U version are also there in the Switch version.
If all you have is a Wii U and looking to play this amazing Zelda game, the Wii U version is definitely not a bad option. The game **does not** make use of the gamepad for things like inventory or maps, which kind of sucks, and the resolution is lower, but it's not enough to make it "unplayable."
FPS does drop, but it happens in both versions, especially the Switch in TV mode.
All in all, the Wii U version is perfectly fine. Just expect slightly longer loads times coming from a disc. But nowhere near the length of load time as Mighty Number 9 for Wii U.