I don't think "more productive" is clear (in the sense of building software on less money). Measuring engineering productivity is basically impossible at this point. But it clearly eliminates a whole class of footguns that are tolerated in C++ just because we need a fast systems programming language.
This is easy to measure because it refers to properties of applications (performance and vulnerability-density) rather than properties of the development process.
Rust also seems to reduce the need for a ridiculous guru at your company to help keep programs correct. That is easy to identify and measure. Haskell doesn't seem to do this. If I imagine running a team of 80 people on a Haskell application vs a Java application, do I feel like I'll need fewer Haskell gurus? No.
This is easy to measure because it refers to properties of applications (performance and vulnerability-density) rather than properties of the development process.
Rust also seems to reduce the need for a ridiculous guru at your company to help keep programs correct. That is easy to identify and measure. Haskell doesn't seem to do this. If I imagine running a team of 80 people on a Haskell application vs a Java application, do I feel like I'll need fewer Haskell gurus? No.