The claim is that learning assembler first will build a better intuition about the inner workings, and thus performance, of the processor.

The reality is that any assembler simple enough to be taught as your first contact with programming will leave you with a wrong intuition about how modern processors work, and thus a wrong intuition about the relative performance of various operations.

Having no intuition about something is better than building a bad intuition, especially at the beginning of your learning journey.