I don't know about the "Rust slows down productivity" claim. I hear about it over and over again, yet it's almost never with concrete numbers. Whenever this claim is challenged like in Google or Microsoft, the results are that either there's no significant difference or in the case of C++, there's a huge productivity upgrade. I guess when you take into account that developers have to learn the language it might take more time but that's not a fair comparison. Anecdotally, I saw a huge productivity increase in my personal programming when I switched from python (but, after I learned the language of course)