A triple daily to LHR in the current climate is clearly excessive but we need to remember that in normal times LHR slots go for $30m+ a pair which would be an absolute non-starter for an airline operating MME-LHR. Wait until things recover and the slots potentially wouldn't be available so maybe the long game is the only way to play this one. However who knows if they can secure the same slots for Summer 2020.
Of course we don't have all the detail but one would hope that the airport has some sort of arrangement with Eastern that will stop them flogging off the slots at the first opportunity when the market eventually picks up.