That still isn't a paradox. Furthermore it still makes sense: a language designed to generate the fastest code has constructs that cannot be compiled quickly, even without optimizations.

But some of it is implementation problems.

Rust's compilation speed issues are not due to optimizations. There is some intrinsic slowness, but also some boneheaded decisions that are now baked in. E.g. the unit of compilation being the crate, not file/module, makes it so you hit some bad scaling laws. And the borrow checker is SLOW, and unavoidably so, but borrow checking could have been avoided with different lifetime rules. Etc.

I say this as a full-time rust developer btw.