Single process python does not take advantage of a multicore architecture but neither would single process mojo. Embarrassingly parallel operations like mandlebrot can trivially be written with multiprocessing (https://github.com/DipanshuSehjal/Mandelbrot-set/blob/master...), or joblib to run in parallel in otherwise vanilla python. It would be trivial to implement this in jax and run on a gpu or tpu, but i wouldn't say that jax is the reason for the speed up.