He's a question that perhaps has been covered - I am a bit short of time so apologies if so.
Nt all A* are the same. I have had kids at a comprehensive and at a super-selective. The comp was a great one for making everyone do citizenship, general studies, BTEC workplace skills and so forth. In some ways this suited DD very well as she was able to make a start on her vocational studies which have led to her current job. But it was deeply disappointing that she was not allowed to do just six or seven GCSEs and aim for grade Cs in English, maths and science: no, she had to take 12 subjects including the above soft subjects waste of time and of course she did badly.
In her case, then, it backfired. But she had a learning disability. Most kids aced their A grades in these easy subjects.
DS1 OTOh did IGCEs in old fashioned subjects- three sciences, maths, a modern language, history. His A levels were all maths and sciences. Kids in his cohort who stayed at the comprehensive did A level drama, media studies, etc.
It really isn't a valid comparison to take the grades and compare them unless they are the grades in the same subjects. That was done, a while back, using the A level grades of the Russell gRoup facilitating subjects. I think there were very very few state nonselectives who got good grades in RG subjects. Barely any got three As at A level. By comparison, grammars and selectives did well.
So, sorry but I think this grade equivalence thing is a bit smoke and mirrors. In fact the whole thread proves to me why it is worth schools picking softer subjects to inflate their grades for league tables. People start to believe the raw grades and forget the subjects.