Small cores are 1.4 GHz not 1.6GHz.. start of GIMP is really slow.. on my OGST image its started in less than 10 seconds and that is even from a standard HDD not even a fast eMMC.
Also you can see the cursor blinking all the time while gimp is loading on the Ubuntu MATE image.
It's probably an un-polished Kernel 4.14 image without the correct armsoc driver/settings they are using

I think HK should really work on improving their images.. the out of the box experience is not very good for beginners

The WebGL test in the video not very good to show "graphics performance" there are better ways to do that.. for example glmark2-es2 or other benchmark..
Although fishgl.com works on my side its terribly slow, and it's so on the Tinkerboard as well.. that should show it's not really optimized in any way (not a surprise considering it's optimized for Microsoft Endge only).
There are other WebGL benchmark that would have been better to show differences.
At least have them compare something like 30~60 FPS rather than 8 vs 12 FPS that's not really showing anything. (for example: https://webglsamples.org/aquarium/aquarium.html)