Eurocontrol really have got this all wrong. If they experience "overdelivery" it's because they've understaffed the sectors concerned for economic reasons. Planning on their part should include the expectation that real world efficient flow of airtraffic includes DCT routes and different FL's flown for fuel economy, therefore traffic will sometimes arrive early.
Who's providing a Service here? Not Eurocontrol or it's Commitees, that's for sure.