> are array languages competitive with something like C or Fortran

The REPL is what matters - also while being performant.

Someone asks you a question, you write something, you run it and say an answer, the next question is asked etc.

I've seen these tools be invaluable in that model, over "write software, compile and run a thousand times" problems which C/Fortran lives in.

Perhaps a more precise question is whether you can write programs as performant as those written in C or Fortran and the answer is it depends on the program (and more likely the programmer). The languages tend to do memory management for you which means giving up some control. Most use “immutable” data structures which force more contraints.

But for the loss of control you get stuff like fancy SIMD implementation for nothing.

All and all there’s a cost/benefit calculation but that ratio can get quite low.