For Delta, JFK will have a lot of traffic heading to New York as well as good connections out of a major hub. ATL will have almost no one going to Atlanta and will be funneling one stop connections. Given almost no one is heading to Detroit or the twin cities compared to say Boston, you have two routes with good point to point in JFK/BOS and one route to mop up connections. Might it not make more sense to think in terms of ATL being upgauged to an A330 over time rather than adding in DTW/MSP? DUB has neither if we're looking for comparison and MAN only has ATL albeit on VS.