I don’t speak with any great expertise, so happy for a teacher to correct, but I think you are right and that BS is not seen as carrying the same weight as economics at A level.
Perhaps it is too vocational, so at this level, like law A level, it can be dry. Someone capable of an 8 in maths should stay on an academic track, build the basics and do the vocational stuff at university or beyond.
You might note that many super selective schools don’t offer BS. They will all offer economics.
Perhaps the problem is the dyslexia. DD is both dyslexic and good at maths. She really did not enjoy school though her maths/science ability got her through. Never finishing class tests, struggling when asked to read something out loud, unexpectedly low marks in an exam because she had misread a question. She went on to read medicine, choosing a course with a lot of early patient contact, but spent last year taking an intercalation degree in engineering. She loved it. The maths, the science, the thinking, and the practical elements. It is the first time she has really enjoyed academics.
It may be worth looking at what is impacting on your sons self esteem. I think it is hard for dyslexics to see themselves as clever, even if they are. Then what he is good at, and what careers appeal. DD at his age was understandably adamant that she did not want to work in an office. She was sporty so started out thinking of being a physio or a PE teacher, till at around 15 it became clear that she was genuinely strong in maths and science and capable of getting the grades required for medicine. And indeed in sixth form, after bouncing around maths sets through her school career based on wonky exam results, she was told it was a real shame she was not taking double maths.
Take theatre studies if he enjoys it and it supports his self esteem. But take two strong academic subjects that keep doors open in case he is a late developer. Both maths and economics can be quite different at A level than GCSE and many find them more interesting.