Anyway, you propably simply mean that a game like breath of the wild running smoothly undocked (in a portable, basically) is impressive, regardless of how it runs when docked.
Yep. Docked performances were completely unrelated.
By the way, i was thinking about RAM configurations.
Wii U has a main pool of 12.8GB/s
Switch is 25.6
Wii U has 32MB eDRAM, we don't know the bandwidth but it's rumored to be around 70GB/s
Switch should have SRAM on die, which thanks to Nvidia's TBR can do a similar job to eDRAM, but we don't know the amount (maybe around 4MB) and the speed, but it's likely faster or at the very least as fast as Wii U's eDRAM.
Now, let's focus for a second on the main RAM. Switch has 2x the bandwidth and a vastly better color compression that reduces even more the bandwidth requirements compared to the old VLIW5 architecture. This to me not only explains why the game is showing such solid performances when undocked, but it's even kind of confirming that the dips in docked mode are bandwidth related. The GPU clocks 2.5x faster when docked so it shouldn't be a problem to handle even 1080p with the handheld frame rate, but the difference in RAM subsystem (especially the amount of eDRAM vs SRAM this time, and the fact that there's stuff that can't be tiled) imho can create some issues in some situations if a higher res is in place and the devs don't find the proper workarounds.
Now, we know that the team started working on this port last spring. It's reasonable in my opinion to assume that they didn't manage to find these workarounds in time, which is why sometimes the frame rate tanks in docked mode while it's solid in portable mode. Now regardless of the fact that it's nothing that ruins the enjoyment of the game (some reactions are a bit extreme), i still think it shouldn't happen because on paper the console should be able to do much more. I can see why it does considering how clearly rushed the Switch launch was, and in fact i'm still wondering if the OS is contributing to the problem to some extent (don't know if you read this but the console kept giving me an error the first 10 times i tried to boot the game, so there's definitely something going on with the software... which is what happens when you basically release a beta) so my hope here is that they acknowledge the issue and keep working on it to fix it in another patch (and a new fw update), because i'm confident that it can be done.