The promise of Julia is that you can have the high-level interface and the low-level code in the same language. The alternative would be coding the low level code in Rust or C and then creating bindings for Python or R.
For a while Julia made the most sense for long-running code that is that is executed almost as often as it is modified (e.g. scientific computing). In this situation Rust or C static compilation times become a hinderance. As ahead-of-time and static compilation features get added to Juliaz this scope will expand.
I really don't want to come across as negative, Julia is a fantastic language, and my hope is that that it will continue its impressive improvement path.
But to follow form the thread's sentiment, I have the feeling Julia lives in an unstable equilibrium. It is lower level than R/Python but doesn't quite deliver the benefits of rust/c/fortran/c++. I find my colleagues gravitate to one of the 2 equilibria.
Maybe your last paragraph crystallizes it. If one lives in the REPL, Julia is wonderful. Not how I work. I prefer the command line. Have new data, run code on it. Data changes in real time, code not. My code may run millions of times on different operating systems and only infrequently change.
What are the things where low-level code is required in Julia, but not in Python/R?
https://github.com/brenhinkeller/StaticTools.jl
I think what we'll end up with is a language that can be used in both a fully static mode and in a dynamic mode along with some possible mixing. We may yet get the benefits of a statically compiled language as the tooling continues to develop. I do not see anything inherent in the language that would prevent that from happening.