I agree that secondary moderns could be centres of excellence. Two of our most exceptional teachers,(Welsh, Latin and Drama) were sec mod teachers. I still remember the retirement speech of the deputy head and the moment he raised his cane (which had been pretty well used during a long career) and snapped it over his head. Many of the youngsters most familiar with it gave the loudest applause and had the most tearful faces! Not sure if that was just romantic sentiment, but it happened. Surely the change then is due to changes in society rather than the fault of the system?
Actually the school still functions rather successfully as a comprehensive and is not bog standard (not much in the way of decent competition from the private sector in Wales), though our 70 acre, fully operational school farm was auctioned off quite a few years ago.