I have learned both and agree with this statement. I think that Rust is harder to learn if you've only worked with high-level, GC languages, and don't have a background doing lower-level programming in C/C++/Obj-C, as well as some experience with functional languages.

Going from something like Java or Python to Rust, one would have a lot to learn.

Hmm I don't think so. Haskell is so fundamentally different to imperative languages that it requires basically throwing away everything you know about programming.

To learn Rust you simply need to understand how values are kept track of by the compiler. Once you develop an intuition for this it's the same as any other modern imperative programming language.