SIMD instructions are used for much more than parallelizing math on primitive types. I think this assumption is whence disagreement on this originates.

It is all of this "other" code where the differences and incompatibilities between SIMD instruction sets become painfully obvious. There are many cases where a good mapping from one SIMD ISA to another doesn't really exist, even between nominally related instruction sets like AVX-512 and AVX2.

The common denominator is sufficiently limited that it doesn't help that much in many cases and in fact may be worse than a use case specific SIMD abstraction that carefully navigates these differences but doesn't generalize.