If you look at some SIMD accelerated algorithms they're anything but simple. They involve clever ways of breaking up the work into streams and clever ways of computing those streams including conditionals without breaking the data flow.
They are very much not the simplest possible implementation of the algorithm and they run an order of magnitude faster for some algorithms.
I do still see their point. SIMD is very rarely applicable, so you could argue that SIMD can only be applied to simple enough code. The idea is: write stupid code because it'll be easier to optimize on a micro level, e.g. with SIMD.
They are very much not the simplest possible implementation of the algorithm and they run an order of magnitude faster for some algorithms.