When something only slightly intense happens, the game just immediately dips to 30fps regardless.
Play in undocked mode and head to a jungle.
This v-sync is probably the reason why it's 720p docked, and has a lower render distance when undocked.
On average, Minecraft on Switch could mantain a higher average framerate than Wii U (even undocked), but this isn't apparent because the Wii U version doesn't drop straight down to 30fps!
Anandtech explains this properly
Performance can be cut nearly in half cases where every frame takes just a little longer than 16.67 ms (1/60th of a second). In such a case, frame rate would drop to 30 FPS despite the fact that the game should run at just under 60 FPS.
are you still having this problem, sometimes I get it too