Being here in DC, I certainly prefer IAD-MUC over IAD-FRA. MUC is simply easier to connect at than FRA. So, I certainly think IAH-MUC should stay so that customers have plentiful options.
I remember reading somewhere a year or two ago that FRA is pretty congested in part because of a night operations curfew. While a curfew should not have any effect upon TATL operations, I believe the point was that there is more room for growth at MUC than FRA.