If you look at the fact that two families have now provided all of Western Europe with most of its indigenous stars at the men's 400 and 1500/mile over the past ten years, you can see that the European decline is not because the African runners are just too good, but because the Europeans gave up. Serious training in large numbers brings success.
The comparison to the basketball family that needs to remain nameless is closer than it seems. While the Ingebrigtsen patron is not a loudmouth always in the news, they did allow the family to be filmed for a long time for a reality tv series (looked pretty good but in Norwegian). And obviously they have three guys right now at sub 4 on one day with Henrik having a 3:30 or 3:31 pr, Filip at 3:32 or 3:33 and now the youngest at 3:58 at 16/250, which is a year ahead of Cram.