So far we know that if you lose any one of Wagner, Kam, or Earl....you lose between 6-8 points a game depending on which time who was out and when. There's a lot to be said about the "inside triangle" of run defense, but IMO, cover 3 lends to a great inside triangle in coverage as well. That's most often those 3 in particular, with KJ Wright sometimes taking the inside zone and Kam taking the flat or the other flip where Earl takes the flat or inside zone, KJ takes whatever's left, and Kam takes deep (robber). All 3 in that triangle need to be able to fill multiple, crucial tasks even outside of the framework of their legacy definitions.
As far as cover 3 goes in general though, coverage is much harder on the inside zones(triangle) vs the outside zones. It's a ridiculous amount of ground to cover and communication & continuity is key. And I say that knowing full well that teams love to flood the sideline at 3 levels against cover 3.