If I go into Ulduar, I dont get the legacy buff. I get it in ICC but not Ulduar. I tested this with Black Temple and Gruul’s Lair as well as Firelands and Bastion of Twilight. Even went and tried Stratholme. Any dungeon or raid that has a timewalking version doesnt get the legacy multiplier. Its kind of annoying not being able to one shot mobs in a vanilla dungeon.