- good quality standard library

- good developer tooling, e.g. a language server

- This is not yet possible, but a good optimiser which can turn an abstract representation of the code into optimal code for a given hardware (CPU or GPU). Currently we are far from this, there is probably a 10x improvement that current compilers can't achieve. See for example a FizzBuzz implementation achieving ~10x throughput improvement after months of optimisation work:

https://codegolf.stackexchange.com/questions/215216/high-thr...

More complex code is likely much more improvable.