Not true at all for me, because in my situation there are some functions which have tight loops that take 99% or more of the execution time. Put the numba decorator in front of them and the code is 100+X faster. Clearly it's not that simple for everyone. But for some people, it can be. So it doesn't make sense to call it a panacea, and it also doesn't make sense to say it doesn't work. It works for some people, not for others.