I'm not sure that the system was ever that near to perfection: for example, John Maddox of Nature didn't like the advent of pre-publication peer review, but that presumably had something to do with it limiting his discretion to approve and desk-reject whatever he wanted. But in any case it (like other aspects of the cozy interwar and then wartime scientific world) could surely never have survived the huge scaling-up that had already begun in the post-war era and created the pressure to switch to pre-publication peer reivew in the first place.