I think that measured by aircraft movements per runway Heathrow is easily the busiest in the world.
In terms of wear and tear on individual strips of concrete, perhaps.
In terms of traffic flow, airports (ORD, MDW, JFK) with crossing runways are often only operating two or three at any one time, so the traffic flow and management problems may be just as "concentrated" as Heathrow's. Depends on a host of factors.