Hello nodadforme,
Unfortunately, I will be
Rejecting your map.
The theme isn't original, as there are many maps relating to minecraft/minecraft blocks/ore etc. Please refer to the document linked in this thread -
https://manacube.com/threads/parkour-list-with-theme.20194/ to make sure your map idea is original.
There isn't really a main build. In the future, try to have one or two main builds for your map, then incorporate the parkour into that, rather than just having blocks floating over the void.
The parkour is very repetitive. There were a few sections with original jumps, but especially near the end, it was mainly just normal block jumps. Try to experiment with a larger variety of blocks and items when building parkour, as well as the way you utilize these, as this will make your map more fun to complete.
The length is good for a hard map, and the difficulty varies throughout the map. Try to stick to one difficulty instead of switching between them, as maps can only be rated as one.
Thanks for submitting your map! I hope to see more maps from you in the future.