The goal is to not need to write C just to get performant code, especially for things like concurrency and numerics. While Nim can be fast without `ref object`, and you can guide the compiler to autovectorize in some cases, it often requires deep knowledge of both the compiler and backend behaviour. That’s not a good developer experience for many users.
Multithreading in Nim is bad to say the least and has been for a while. The standard library option for multithreading is deprecated, and most alternatives like weave are either unmaintained or insanely limited (taskpools, malebolgia, etc.). There's no straightforward, idiomatic way to write data-parallel or task-parallel code in Nim today.
The idea of the project is to make shared-memory parallelism as simple as writing a `parallel:` block, without macros or unsafe hacks, and with synchronization handled automatically by the compiler.
Course, performance can be dragged out of Nim with effort, but there's a need for a language where fast, concurrent, GC-optional code is the default, not something one has to wrestle into existence.
FWIW, I almost always have to look at the generated assembly (never mind C) to even verify things are vectorized. I hope you realize the promise of a PLang where that doesn't need checking or some kind of "autovec-miss" compiler flags or so on and wish you all the best.
I'm curious if you have looked at Chapel: https://chapel-lang.org/
If not, you might find some thing there inspiring.