Do you say that from the perspective of compiled languages? I hear good things about .net core wrt SIMD, but that has the advantage it can decide at JIT.
I'm not the person you're asking, but I share that opinion for both compiled languages and JIT solutions, including .net core specifically. All but the most trivial use cases can't be autovectorized, by JIT or otherwise. One of the recent things I worked on (reed-solomon decoding) offers basically zero opportunities for autovectorization unless the compiler reinterprets certain scalar loops as dedicated galois instructions on AVX512F hardware, but that optimization isn't implemented, it wouldn't help other architectures anyway, and it's still 10x slower than a well thought out vectorized approach.