I don't know if you've seen the research, but teacher assessment is notoriously unreliable.
I had a lot turned off Alevel maths after we did our mocks in November. Students were pretty horrified by the difficulty of the new papers
So under the old system from what Noble and others are saying,
- teachers cannot assess the potential ability of their own students for A level maths, (I suspect because they just used GCSE past paper questions and don't try giving more stretching questions which pick out potential)
- students are put off by difficulty and in the mindset that they need to be able to recognise and do with ease all the questions on the paper.
So generally students have not developed the resilience or confidence required to persevere when problem solving gets hard and they are not scoring high marks even if they enjoy the subject. Plus they don't have faith in their teachers to tell them if they are on the right track.
No wonder so many students are underprepared for tackling difficulty at A level and beyond.
I think that this is one thing that certain selective public schools do better. They regularly give very hard questions or exam papers where many students score poorly but this does not prevent most students doing maths in the sixth form and getting very good grades.
Noble it is the past system that has created the situation of this temporary fall in take up of maths this year. GCSE students have been taught that lack of mistakes is the primary aim of a subject like maths. Teachers rely on public exam results and grade boundaries rather than their own teaching judgement so that is what the students and their parents place most confidence in rather than what the teachers say about their ability.
You hopefully will embark on a change that means that this is only temporary and potential STEM students will not be set up to feel inadequate later on in their education.
Plus the other subjects will catch up with the new grading system so it may well swing the other way.