what's the point of using Rust, Go, etc. for speed when

you can just write Python all the way down and write C++ modules (Boost::Python) for the slow parts as needed in the same way numpy works.

if you need everything to be fast and scalable, then just use Java.

I don't see any use case for Go, Rust, Haskell, and other compiled shitlangs that aren't C/C++.

C++: spending 10 hours to make your program take 3 seconds less to start up

Python: spending very little time to develop a program that is ``slow'' in terms of CPU cycles

What's more important: CPU time or developer time? I'd say the latter.