Before Forsaken launched, Bungie told us that Xur would only sell year 1 exotics and Fated Engrams would only drop year 1 exotics. It's in the release notes. Also this isn't actually changing a mechanic. Fated engrams could always give you duplicates if you already owned every weapon and class-specific armor piece on the character you used to purchase an engram. Since you had all year 1 items you could get on your character, it worked as intended.