I think that, if we go down the 'what is education about?' line (perhaps creating a myth of an inspiring teacher who creates a love of the subject in all their pupils by exploring way beyond the syllabus ... but as a result then has to be somewhat unscrupulous in their approach to passing the required exams) then we run into the issue of fairness.
Is it 'fair' that a brilliant but maverick educator should be 'allowed' to play fast and loose with the rules of a niche qualification, while 'normal teachers' in 'normal schools' have to mind their ps and qs and be careful in following the rules of a more mass qualification? In particular, is this 'fair' when the two qualifications are regarded as equal when to comes to university admissions?
If a school wishes to pride itself in the depth and quality of its education beyond the syllabus (which to be fair it absolutely should, at a minimum, because it has many times the funding per student), that is fine, and as a result many of its pupils will go on to be successful both in applying to universities where interviews are required, and in their future careers. However, the 'on paper qualifications' should be the same, and acquired under exactly the same controlled conditions, as everywhere else.
I read this story more as evidence of the extreme pressure that must be put on such schools by their parental body to ensure 'the success that we have paid for'. I have British-educated acquaintances who have taught at top American universities, who have been attacked by students for 'not giving the right grades - the grades I pay my fees for', and I can see that parents who have paid the fees as a British public school could feel they have a right to top grades, as a simple commercial transaction. Enabling that to happen - by selecting specific qualifications where success can be more certainly predicted or manipulated, by fair means or foul - becomes a commercial imperative for such schools.