Just with Zelda, we can tell it's a lot more powerful when undocked, you have the same resolution as the wii u, but almost always locked frame rate, where wii u is constantly dropping, this was a game built on the wii u and ported to the Switch in less than a year according to their GDC talk this year.
It's anywhere from 1.5x to 2x faster as a handheld and twice that when docked, this is not getting into mixed precision which could get pretty close to current gen consoles when docked when everything is taken into account.
The real port problem with the switch is that the cpu clock is too low, it's much faster than wii u's cpu, but it's only giving about 50% of what devs on the ps4 have for instance.
For anyone looking for a comparison with Xbox 1, when undocked, it is 20% to 35% of xb1's performance and double that when docked, of course the higher the range, the more mixed precision is being utilized. Switch would have been closer with pascal, but it isn't much closer, something like 25% to 40% when undocked and double that when docked.