Is it "for new code which is maths/vector heavy and not relying on any existing environment, Julia is a valid competitor to pypy"? Or is there a better qualifier?
99%? You won't get the most recent versions because a lot of packages started requiring v1.3 when the new AD and multhreading mechanisms came out, but you can still boot up the LTS and run any standard analysis that existed back when 1.0 was around, which is something like 3000+ packages. Where is your FUD coming from?
Also I should note that Julia performance greatly improved since. Next week there should be the 1.6.0 release, which will have even better numbers.
https://benchmarks.sciml.ai/html/MultiLanguage/wrapper_packa...
https://gist.github.com/ChrisRackauckas/cc6ac746e2dfd285c28e...
https://gist.github.com/ChrisRackauckas/4a4d526c15cc4170ce37...
are the ones from the top of my head.