I think its wrong to presume that WC level has decreased just because we don't see the same old familiar faces trashing through the stages.
We are passing the era of classic football, if this last 3 years have shown something is that strategy/tactics and physical play are becoming more and more fundamental not only in creating play but also to counter/eliminate plays from opposition. (LvG changed the formation 3 times in the match vs Mexico, Kyut was a turbo puppet.)
Forget the "ok guys, do what you do" chitchat, oldschool cats can't survive in this. A context of high demand for physician/coaching staff tends to create efficient players that suit a particular gameplay. Sometimes these players are no technical beasts but horses of secondary skills like workrate/pressing/defending. Put it like this: The sport is creating more athletes and less geniuses, therefore creating more solid teams in the physical aspect. This makes creative football a.k.a possession/tikiflop/whatever less of a rule, and teams tend to balance or incline to certain style depending on what they have available.
Forget your romantic views of football, your favorite oldschool players could not adapt to this kind of physical demand along with the calendar. That's why the likes of Xavi & Pirlo are dinosaurs today, because aside their magnificent talent they fail to the question: Ok, but can you run?
Now you have teams like Switzerland, Costa Rica, Greece, Algeria, Nigeria and US going to round of 16. Not all of them play the same, but what is the common denominator?