Also, Eston was in a federation with BoM and Norland long before Darka attacked Masillion. Darka chose to attack Eston when Eston's allies were busy defending Falasan against CE. They took the Masillion duchy when they knew that they would get away with it, plain and simple.
As I was the ruler of Darka back then I can tell you we didn't give a damn what Estons allies were doing(well, apart from Talerium, but they were our ally as well). What we cared about was them plotting an attack against us. We just made the first move to knock some sense into Eston about not listening to Norland.
As a result Eston lost Malor, Tintar and Massillion. In the peace treaty they renounced any and all claim to those regions. In exchange Darka paid them a sizable amount of gold and helped them take Amriel, Barad Riel, Elost, Moramroth, Hernepoole, Ashmoor and I think even Belegrond. Eston could have had Brackhead too. We essentially offered them the entire Norland on a silver platter.
So forgive me about being tired of hearing poor Eston complaining about losing three regions when in return they gained two times what they lost. I fully consider Massillion duchy payment for mercenary services Darka gave Eston.