> Which still means you have to write your code at least thrice, which is two times more than with a variable length SIMD ISA.

This is a wrong approach. You should be writing you code in a high-level language like this:

    x = sum i for 1..n: a[i] * b[i]

I don't understand what is the advantage of writing the SIMD code manually. At least have a LLM write it if you don't like my imaginary high-level vector language.