You're usually best able to explain something just after you learned it yourself. After a while you forget what was difficult about the thing you learned.
A C programmer, a Python programmer and a Java programmer should write the book together, with expert insight from a Rust pro.
I'm not sure I agree with the anecdote in your first paragraph, and indeed I preemptively addressed it in my comment: one's own experience is just one way in which something can be hard to learn, whereas people who are regularly teaching and interacting with beginners have a broader view on what people find hard. My experience is, broadly speaking, good teachers are those that have had a lot of practice teaching their material.
A C programmer, a Python programmer and a Java programmer should write the book together, with expert insight from a Rust pro.