While the concept is great, I think the map would really benefit from having a sense of direction. The very first part where you're in the house and have to make your way through the little caves is great. I would even recommend making it so you have to parkour from the stairs of the house to the stairs of the fist cave. It would be a great use of the space and make it so you aren't running across a full plot needlessly. Without that parkour there, you may as well have had them spawn in the start of the first cave. Since, although the rest of the first plot looks great, it really adds no value to the parkour.
The withers themselves are great. I love the way you incorporated the parkour into them and have a clear storyline. I also love the terrain of the nether section you have. After I saw the first plot I was able to immediately recognize that Cursus made the terrain, and I expected great things from the rest of the terrain. I was not disappointed there!
The hardest part about this map is figuring out where to go. I spent 10 minutes trying to figure out where to go after the dropper, and got lost multiple times. I then went to one of the checkpoints to try and see if there was something I was missing, but no, I still had a very difficult time figuring out the path. There is just so much going on in this map that the carpets and arrows get lost in the background. While you may have a great sense of where to go, you made the parkour. Having never seen the map, it was more confusing than other parkours that I already receive complaints about the path not being clear enough. You shouldn't need an arrow after every 4-10 jumps telling you where to go. It should be clear enough by the design of the parkour. A little bit of added direction through arrows is fine, especially in spots that are confusing or where there are barriers, but this parkour just feels way too confusing. I like the theme, and I like the look of the map, but the parkour path needs to be drastically improved before I can accept this map.
As a side note, with a parkour like this that interweaves with many different elements, it is extremely difficult to test for any shortcuts or skips. If you do decide to rework the path, I would suggest being 100% sure there are no shortcuts.