Clunky writing writing can be explained away with "readers are dull and lazy." Whether that's the case or the author has not found a user-friendly & medium appropriate way to work through difficult material... Concluding the latter is likely to produce the best book.
Brian Greene wrote a fantastic walk through of special relativity. He used the "atomic pong on a moving training" that will take an ordinary reader from speed of light invariance to time travel. It was (iircc) a few pages, one picture (the atom bouncing on a train). Incredible bit of pop-science writing.
From there, you can grok what "time flips in a black hole."
Assuming readers (or users) are stupid is just a lot less likely to result in better writing. Concluding that your writing can be easier to understand is.