From having played the game a lot during the development I can say that I completely agree with your point. The combination of flaws in the level design and the slow character acceleration when jumping does make for a rather unrewarding difficulty. To add on top of this is the lack of being able to have multiple attempts at a level before losing.
A random level order was chosen to give the impression of each level being its own dream, where the dreams would not necessarily always occur in the same order. In retrospect I do agree that it would have been better to stick to a fixed level order, especially as the level difficulties turned out to be so very different from each other.