Fair point. I could have placed a greater emphasis on ownership and mutability being two separate axes.

That said, I think you downplay the ways that references and mutability do interact in Rust. If there is a single outstanding reference to a value, Rust won't let anyone mutate the underlying value. I think this is quite an important part of Rust to understand that's not obvious to someone who's new and especially coming from a language that enforces no such guarantees about mutability.