This is a very good point, fast compilation times are a huge benefit. The slow compiler is a downside of languages like Rust, Scala, and Haskell. Especially if you have many millions of lines of code to compile like Google.

However, OCaml has a very fast compiler, comparable in speed to Go. So a more expressive type system is not necessarily leading to long compilation times.

Furthermore, Scala and Haskell incremental type checking is faster than full compilation and fast enough for interactive use. I would love to see some evidence that Golang devs are actually more productive than Scala or Haskell devs. So many variables probably influence dev productivity and controlling for them while doing a sufficiently powered experiment is very expensive.