The “Revive the Might and Magic universe” project.

1) The burial mounds were built under Rilos on the orders of Mysterio, because although Mysterio won, he still respects them and therefore buried them in the mounds. 2) Okay, but let's assume that's the case, as Tarkin's cities will appear throughout the campaign, and each mission will require eliminating them. Even when the Krigans arrive. 3) But the difference remains; they are still a threat to the mission.