We don't have to speculate on this. PISA research has described that effective teachers should adapt their teaching and also why a system like in Romania is a bad idea for the society (except for the elites). It is the second poorest country of the Union and one of the most unstable. The data and research is all public. It's not a popular opinion with this crowd here - but then you can argue against the science instead of populist opinions..

I might be wrong here, but I never heard that PISA has proved that averages matter more than top results, I thought that's just the axiom they are basing their assessments on.

I understand why fostering top performants is a hard sell in a globalised society though. Poor countries will lose top talent to rich countries anyway, and rich countries can rely on the stream of talent from the outside. For the scientific progress of humanity as a whole, having geniuses matters more than rising average level IMO though