So the brighter and more motivated dc were kept down? Not allowed to progress by deliberate action?
The problem with this statement is the idea that the only thing to learn is the curriculum, and there's no value in learning other stuff - or simply going deeper into stuff already covered.
That's clearly bunkum, the motivated and advantaged students will still get huge benefits from going deeper into what they've already learnt, or self motivatedly taking themselves into other new areas.
Now for a few subjects very close to exams - where self directed learning is tricky, and there's now a shortage of time to teach the rest of the curriculum then there may be more loss, but the situation with GCSE / A Levels and 2021 are going to be badly compromised anyway, and just teaching the few able to access would not really have been equitable.