It features the tegra x2 which has 750gflops in 32bit floatingpoint and 1,5 teraflop in 16bit floatingpoint. The Wii U only has 175gflops of floating points and has no acces to running two 16 floating points operations at the same tome like the PS4pro and Switch do,  what possibly  gives it a little extra power, because simple operations could be run in 16 floating points. The CPU should also be a big power up since the Wii U cpu was terrible, it features more ram 4gb according to the rumors (Emily).  But ifwe only count rough GPU power and disregard the tech is newer it's a little bit over four times as powerful.

It doesn't feature Tegra X2 though, it features a custom Tegra for which we have no specifications as yet. 

In terms of RAM, the difference will likely be 3GB for games on Switch versus 1GB in Wii U, so a factor of three.

Well, it's official now: Zelda runs on Switch at stable 30 fps with no dips, and Wii U version runs at 20 fps.
What the fuck, Nintendo?

That's assuming the Wii U version doesn't get any optimization before release, which I'm sure it will. It wouldn't make sense to make one version perform worse than the other.

I have a new theory: considering the team has a Switch dev kit early in the dev process (or so I remember reading from Aonuma himself), they really started to experiment with the new tech, but due to their promise of the game coming to the Wii U, they have to cut expectationes and some parts of the game (like maybe effects and of course frames) to be able to run on the Wii U.

Also, the extensive experience of the Digital Foundry is that the Wii U version does not run at a consistent 20fps.  It has a good number of problems and dips, but it does run better than everyone keeps making it out to.