Not necessarily true with Julia. Many libraries like DifferentialEquations.jl are Julia all of the way down because the pure Julia BLAS tools outperform OpenBLAS and MKL in certain areas. For example see:

https://github.com/YingboMa/RecursiveFactorization.jl/pull/2...

So a stiff ODE solve is pure Julia, LU-factorizations and all. This is what allows it to outperform the common C and Fortran libraries very consistently. See https://benchmarks.sciml.ai/html/MultiLanguage/wrapper_packa... and https://benchmarks.sciml.ai/html/Bio/BCR.html